As previously mentioned, I've been trying to track down the change that caused my GL_POLYGON_OFFSET_FILL /depth buffer issue. This was working fine for many years until recently. I've narrowed it down to something that changed between b224 and b226 (225 also, but that seems to be a partial build). When I try to track this back to hudson, the dates/times don't seem to tie up with anything relevant. So I'm suspecting the change was actually 1 day earlier. 'choose and use graphics capability' (96af6c9bf2d683115996214cd895f9f9ef7ceea6)
Further testing has shown that prior to 225 a 24bit depth buffer was selected automatically, after that date only a 16bit buffer is selected. So it seems like the code fails to detect the best available? If I manually select 24bit in my request, then things are working again :)