I see, then enabling letterboxing might be a good temporary solution, since you wouldn't have to change the fontsize then (hopefully).
Was it after the mentioned implementation (one page earlier), when the bug occured? I'm asking, since I'm still using clsid's svn 843 (icl 9, sse) and won't upgrade to a version with buggy subtitles, because I use them too often.
Btw. Whole lot of good work on ffdshow, guys! Much appreciated.