In the QDialog constructor it's possible to give a parameter of type Qt::WindowFlags. However giving anything else besides Qt::Dialog will cause a window server panic 64 ("An attempt was made to set a transparency operation to a window that has not been enabled to be transparent").

The documentation of the flag Qt::Dialog states that "This is the default type for QDialog". Thus the API very much looks like the flags can be changed and the Qt implementation can't assume that a QDialog will always have Qt::Dialog. In any case it must not crash.

The attached application can be used to reproduce the panic.