QDialog exec() crashes in XCode if GuardMalloc is enabled

Steps to reproduce:

• prepare the "dialogs/standarddialogs" example:

• With QT 4.8.4 installed, use qmake to generate the xcode project for "dialogs/standarddialogs" example: qmake -spec macx-xcode
• open the project in xcode and compile it.

• Enable GuardMalloc

• In xcode, choose "Edit Scheme..."
• In the diagnostics Tab, check the box "Enable Guard Malloc"

• Run the example.
• Click on the button "QInputDialog::getInt()"
• Press "Cancel"

Result:
It crashes.