In Creator GDB hangs on a QtWidgets application

When I try to debug my application with GDB it hangs infinitely right after it loaded. Debugging the very same executable from console works fine.

I turned off loading of .gdbinit and the Debugging helpers, too. No python process is running while GDB is waiting.

When trying to pause it or, after it, setting a breakpoint I get the following:

dATTEMPT SYNC
dATTEMPT BREAKPOINT SYNCHRONIZATION
dTAKING OWNERSHIP OF BREAKPOINT 1 IN STATE 0
dRUNNING NEEDS-STOP COMMAND -break-insert -f "\"main.cpp\":1620"
dCHILD ALREADY BEING INTERRUPTED. STILL HOPING.
dBREAKPOINTS ARE NOT FULLY SYNCHRONIZED

Interestingly, after 10+ minutes the program continues to run until the breakpoint but Creator cannot react to it properly: while querying the variables in the Debug view it shows a "GDB is not responding" dialogue.

I also gdb'd into GDB while it was hanging. I attach the output from there, too.