Adding a breakpoint breaks the code?

I have encountered an issue where it seems that setting a breakpoint in Qt Creator changes the behavior of the program. In my case it crashes what I'm trying to debug making the debugger unusable.

The issue should be reproducable with the the patch I was trying to debug when the problem appeared. I have tried sereral times and was able to repeat it every time.

Reproduction steps:

• checkout qt5 at b1ce3549a0f7378465a57173301281a1c9dbe0ba
• checkout qtdeclarative at https://codereview.qt-project.org/c/qt/qtdeclarative/+/502174/
• ninja Quick qmlcachegen qmlimportscanner
• configure reproducer project Truc
• ninja -v
• copy the arguments of the second qmlcachegen invokation starting with --bare (should be step 10/18)
• set the creator run target to qmlcachegen and set its arguments to the ones just copied
• set a breakpoint on QQmlJSTypePropagator::generate_GetOptionalLookup in qmljstypepropagator.cpp
• run in debugger
• the code should run as expected without the breakpoint but assert with it.

I have attached a video demonstrating the bug.

I have only one kit: