I was not able to find any configure or CFLAGS definitions at your links... Also I thought winehq provides builds which differ from Debian official builds. However I found compile flags in the output here: https://build.opensuse.org/package/live_build_log/Emulators:Wine:Debian/wine... (which is referenced from winehq). Options are similar to mine, but the stack frame cleanup code differs (lea in the manually built Wine vs sub in the packaged version), likely due to different compiler versions. It seems the old game app in question was compiled with some exotic compiler, as I found explicit "clc" instructions in all function call wrapper epilogues, except for one, which led to the issue. In any case relying on the Carry flag seems wrong since it's fragile and can be easily influenced by various compiler options. Assuming it's an app bug, closing this thread.