I’m stumped. I just checked this on my Arch Linux setup, and my Win10 MSYS2 laptop, everything works as expected. But given the issues raised in this thread, there’s a suggestion of a funny interaction with Qt5 that might be causing issues. Maybe you could try removing the Qt5 development packages, installing the Qt4 equivalent packages, then running ./configure and ./build again, and see if that fixes the issue?
Otherwise, I’ve no idea how the same binary executed within the Qt debugger could possibly behave differently outside of it. But it does suggest a potential memory issue, I’ll have a look into that next week if I find the time…