The docs state that “Permissions that do not make sense on certain platforms are ignored on those platforms.” Looking at the code, the mode is set up on Windows, but it does go through _wchmod which probably doesn’t translate 100% to what you’re looking for.
I suspect that the install tree (prior to packaging) may be getting the right permissions, but QtIFW doesn’t know that the perms are “important” and translate that into actual action after installation.