QFileDialog Crashes application on deleting multiple folders

I need to create a custom dialog box with password feature to save a file. It's working fine fine but If I try to open dialog box and in that If I delete and create multiple folders around 20 times or more than that then it crashes. I am not getting why does it crashes on calling exec() function for QFileDialog. Please help.

More information provided at this link
https://stackoverflow.com/questions/52989917/qfiledialog-crashes-application-on-deleting-multiple-folders