The fix for the vc7 libc putenv bug is also needed here to avoid a crash.

ext/standard/basic_functions.c

@@ -886,6 +886,13 @@ zend_module_entry basic_functions_module = {
 static void php_putenv_destructor(putenv_entry *pe)
 {
 	if (pe->previous_value) {
+#if _MSC_VER >= 1300
+		/* VS.Net has a bug in putenv() when setting a variable that
+		 * is already set; if the SetEnvironmentVariable() API call
+		 * fails, the Crt will double free() a string.
+		 * We try to avoid this by setting our own value first */
+		SetEnvironmentVariable(pe->key, "bugbug");
+#endif
 		putenv(pe->previous_value);
 	} else {
 # if HAVE_UNSETENV