https://bugs.winehq.org/show_bug.cgi?id=39637
--- Comment #5 from Dmitry Timoshkov dmitry@baikal.ru --- (In reply to Dmitry Timoshkov from comment #4)
There are already the tests showing that GetClassInfo() for user32 classes should not set CS_GLOBALCLASS bit. But the application wraps GetClassInfo() call by ActivateActCtx()/DeactivateActCtx(), probably that makes it behave differently.
That activation context belongs to comctl32.dll, probably comctl32 registers the "Button" class with CS_GLOBALCLASS.