Compiler ABI is reset from "custom"

I have a MinGW 4.8.1 from http://sourceforge.net/projects/mingwbuilds/, which is a 64-bit compiler, but obviously reports the wrong ABI, at least QtCreator detects it as 32-bit. The binaries built by this gcc in fact are 64-bit (from sizeof(void*)!).

So to work around this, I set the ABI version in QtCreator to custom and changed the last commbobox from 32 to 64-bit. Then everything works fine.

Unfortunately QtCreator forgets this setting when I restart it. After the restart it seems to reread the ABI from the compiler and overwrites my custom settings ...