diff --git a/libs/kimath/src/geometry/shape_line_chain.cpp b/libs/kimath/src/geometry/shape_line_chain.cpp
index 242c2adbdc..af7059c022 100644
--- a/libs/kimath/src/geometry/shape_line_chain.cpp
+++ b/libs/kimath/src/geometry/shape_line_chain.cpp
@@ -305,11 +305,36 @@ void SHAPE_LINE_CHAIN::Replace( int aStartIndex, int aEndIndex, const SHAPE_LINE
     if( aStartIndex < 0 )
         aStartIndex += PointCount();
 
+    // We only process lines in order in this house
+    wxASSERT( aStartIndex <= aEndIndex );
+
+    SHAPE_LINE_CHAIN newLine = aLine;
+
+    // It's possible that the start or end lands on the end of an arc.  If so, we'd better have a
+    // replacement line that matches up to the same coordinates, as we can't break the arc(s).
+    ssize_t startShape = m_shapes[aStartIndex];
+    ssize_t endShape   = m_shapes[aEndIndex];
+
+    if( startShape >= 0 )
+    {
+        wxASSERT( newLine.m_points.front() == m_points[aStartIndex] &&
+                  aStartIndex < m_points.size() - 1 );
+        aStartIndex++;
+        newLine.Remove( 0 );
+    }
+
+    if( endShape >= 0 )
+    {
+        wxASSERT( newLine.m_points.back() == m_points[aEndIndex] && aEndIndex > 0 );
+        aEndIndex--;
+        newLine.Remove( -1 );
+    }
+
     Remove( aStartIndex, aEndIndex );
 
     // The total new arcs index is added to the new arc indices
-    size_t            prev_arc_count = m_arcs.size();
-    std::vector<ssize_t> new_shapes     = aLine.m_shapes;
+    size_t               prev_arc_count = m_arcs.size();
+    std::vector<ssize_t> new_shapes     = newLine.m_shapes;
 
     for( ssize_t& shape : new_shapes )
     {
@@ -318,8 +343,9 @@ void SHAPE_LINE_CHAIN::Replace( int aStartIndex, int aEndIndex, const SHAPE_LINE
     }
 
     m_shapes.insert( m_shapes.begin() + aStartIndex, new_shapes.begin(), new_shapes.end() );
-    m_points.insert( m_points.begin() + aStartIndex, aLine.m_points.begin(), aLine.m_points.end() );
-    m_arcs.insert( m_arcs.end(), aLine.m_arcs.begin(), aLine.m_arcs.end() );
+    m_points.insert( m_points.begin() + aStartIndex, newLine.m_points.begin(),
+                     newLine.m_points.end() );
+    m_arcs.insert( m_arcs.end(), newLine.m_arcs.begin(), newLine.m_arcs.end() );
 
     assert( m_shapes.size() == m_points.size() );
 }
@@ -328,6 +354,7 @@ void SHAPE_LINE_CHAIN::Replace( int aStartIndex, int aEndIndex, const SHAPE_LINE
 void SHAPE_LINE_CHAIN::Remove( int aStartIndex, int aEndIndex )
 {
     assert( m_shapes.size() == m_points.size() );
+
     if( aEndIndex < 0 )
         aEndIndex += PointCount();
 
@@ -1025,7 +1052,7 @@ SHAPE_LINE_CHAIN& SHAPE_LINE_CHAIN::Simplify( bool aRemoveColinear )
         const VECTOR2I p1 = pts_unique[i + 1];
         int n = i;
 
-        if( aRemoveColinear )
+        if( aRemoveColinear && shapes_unique[i] < 0 && shapes_unique[i + 1] < 0 )
         {
             while( n < np - 2
                     && ( SEG( p0, p1 ).LineDistance( pts_unique[n + 2] ) <= 1
diff --git a/pcbnew/router/pns_dragger.cpp b/pcbnew/router/pns_dragger.cpp
index d9b05375a6..59f3824d61 100644
--- a/pcbnew/router/pns_dragger.cpp
+++ b/pcbnew/router/pns_dragger.cpp
@@ -89,15 +89,23 @@ bool DRAGGER::startDragSegment( const VECTOR2D& aP, SEGMENT* aSeg )
     else if( distB <= w2 )
     {
         //todo (snh) Adjust segment for arcs
-        m_draggedSegmentIndex++;
+        if( ( m_draggedSegmentIndex < m_draggedLine.PointCount() - 1 ) &&
+            ( m_draggedLine.CLine().CShapes()[ m_draggedSegmentIndex + 1 ] < 0 ) )
+        {
+            m_draggedSegmentIndex++;
+        }
+
         m_mode = DM_CORNER;
     }
-    else if ( m_freeAngleMode )
+    else if( m_freeAngleMode )
     {
-        if( distB < distA )
+        if( distB < distA &&
+            ( m_draggedSegmentIndex < m_draggedLine.PointCount() - 1 ) &&
+            ( m_draggedLine.CLine().CShapes()[ m_draggedSegmentIndex + 1 ] < 0 ) )
         {
             m_draggedSegmentIndex++;
         }
+
         m_mode = DM_CORNER;
     }
     else
diff --git a/pcbnew/router/pns_line.cpp b/pcbnew/router/pns_line.cpp
index 1df6351ef7..9ac2a138a9 100644
--- a/pcbnew/router/pns_line.cpp
+++ b/pcbnew/router/pns_line.cpp
@@ -587,6 +587,22 @@ void LINE::dragCorner45( const VECTOR2I& aP, int aIndex )
 
 void LINE::dragCornerFree( const VECTOR2I& aP, int aIndex )
 {
+    const std::vector<ssize_t>& shapes = m_line.CShapes();
+
+    // If we're asked to drag the end of an arc, insert a new vertex to drag instead
+    if( shapes[aIndex] >= 0 )
+    {
+        if( aIndex > 0 && shapes[aIndex - 1] == -1 )
+            m_line.Insert( aIndex, m_line.GetPoint( aIndex ) );
+        else if( aIndex < shapes.size() - 1 && shapes[aIndex + 1] == -1 )
+        {
+            aIndex++;
+            m_line.Insert( aIndex, m_line.GetPoint( aIndex ) );
+        }
+        else
+            wxASSERT_MSG( false, "Attempt to dragCornerFree in the middle of an arc!" );
+    }
+
     m_line.SetPoint( aIndex, aP );
     m_line.Simplify();
 }
diff --git a/pcbnew/router/pns_node.cpp b/pcbnew/router/pns_node.cpp
index 995cb3b8a1..478e1df0e9 100644
--- a/pcbnew/router/pns_node.cpp
+++ b/pcbnew/router/pns_node.cpp
@@ -943,13 +943,15 @@ const LINE NODE::AssembleLine( LINKED_ITEM* aSeg, int* aOriginSegmentIndex,
     LINKED_ITEM* prev_seg = NULL;
     bool originSet = false;
 
+    SHAPE_LINE_CHAIN& line = pl.Line();
+
     for( int i = i_start + 1; i < i_end; i++ )
     {
         const VECTOR2I& p  = corners[i];
         LINKED_ITEM*    li = segs[i];
 
         if( !li || li->Kind() != ITEM::ARC_T )
-            pl.Line().Append( p );
+            line.Append( p );
 
         if( li && prev_seg != li )
         {
@@ -960,11 +962,17 @@ const LINE NODE::AssembleLine( LINKED_ITEM* aSeg, int* aOriginSegmentIndex,
                 const ARC*       arc = static_cast<const ARC*>( li );
                 const SHAPE_ARC* sa  = static_cast<const SHAPE_ARC*>( arc->Shape() );
 
-                int nSegs = pl.Line().SegmentCount();
+                int      nSegs     = line.PointCount();
+                VECTOR2I last      = line.CPoint( -1 );
+                ssize_t  lastShape = line.CShapes()[nSegs - 1];
+
+                line.Append( arcReversed[i] ? sa->Reversed() : *sa );
 
-                pl.Line().Append( arcReversed[i] ? sa->Reversed() : *sa );
+                segIdxIncrement = line.PointCount() - nSegs - 1;
 
-                segIdxIncrement = pl.Line().SegmentCount() - nSegs - 1;
+                // Are we adding an arc after an arc? add the hidden segment
+                if( lastShape >= 0 )
+                    segIdxIncrement++;
             }
 
             pl.Link( li );
diff --git a/pcbnew/router/pns_optimizer.cpp b/pcbnew/router/pns_optimizer.cpp
index 17fa10fad8..238f46d260 100644
--- a/pcbnew/router/pns_optimizer.cpp
+++ b/pcbnew/router/pns_optimizer.cpp
@@ -561,7 +561,8 @@ bool OPTIMIZER::mergeFull( LINE* aLine )
 
 bool OPTIMIZER::mergeColinear( LINE* aLine )
 {
-    SHAPE_LINE_CHAIN& line = aLine->Line();
+    SHAPE_LINE_CHAIN&          line   = aLine->Line();
+    const std::vector<ssize_t> shapes = line.CShapes();
 
     int nSegs = line.SegmentCount();
 
@@ -570,7 +571,7 @@ bool OPTIMIZER::mergeColinear( LINE* aLine )
         SEG s1 = line.CSegment( segIdx );
         SEG s2 = line.CSegment( segIdx + 1 );
 
-        if( s1.Collinear( s2 ) )
+        if( shapes[segIdx] < 0 && shapes[segIdx + 1] < 0 && s1.Collinear( s2 ) )
             line.Replace( segIdx, segIdx + 1, s1.A );
     }