XP codec pack ??
Anyhow: If I'm informed correctly best "Rendering mode" for w7 is EVR.
(rightclick >) Options > Preferences > Video > [Video rendering]
Further: did you try "Use new subtitle parser/renderer " respectively "Enable drawing subtitles under image with EVR renderer"?
(rightclick >) Options > Preferences > Subtitles [Subtitle properties]
P.S.: Build 1031 is out already.