https://bugs.winehq.org/show_bug.cgi?id=55439
--- Comment #3 from Rafał Mużyło galtgendo@o2.pl --- ...my personal guess would be that certain values of WINEDEBUG open a console handle regardless of that change.
WINEDEBUG does have its own set of quirks, like the fact that if you set 'server', it's stays set across *all* terminals until you explicitly unset it.
While ruby makers technically aren't console apps, most of their non game-specific code is an embedded ruby interpreter. As the most simple way for scripts to communicate somethings is to print something to stdout, many custom script tend to do exactly that. The way it works on Windows, such output is suppressed *unless* the maker is running in debug mode. wine's way of not opening stdout in the first place might not be the correct approach.
Out of curiosity, mind telling what that script line exactly is ?