Restore a side-effect that the router appears to depend on.

pcbnew/router/pns_item.h

@@ -222,7 +222,7 @@ public:
         return Shape();
     }
 
-    virtual void Mark( int aMarker ) const { m_marker |= aMarker; }
+    virtual void Mark( int aMarker ) const { m_marker = aMarker; }
     virtual void Unmark( int aMarker = -1 ) const { m_marker &= ~aMarker; }
     virtual int Marker() const { return m_marker; }
 

pcbnew/router/pns_router.cpp

@@ -307,7 +307,7 @@ void ROUTER::markViolations( NODE* aNode, ITEM_SET& aCurrent, NODE::ITEM_VECTOR&
         {
             int clearance = aNode->GetClearance( item, obs.m_item );
             std::unique_ptr<ITEM> tmp( obs.m_item->Clone() );
-            tmp->Mark( MK_VIOLATION );
+            tmp->Mark( tmp->Marker() | MK_VIOLATION );
             m_iface->DisplayItem( tmp.get(), -1, clearance );
             aRemoved.push_back( obs.m_item );
         }