Compressor won't show subtitles in preview

I'm using compressor to generate an itunes package.

I've added the uncompressed quicktime movie, the trailer, a closed caption file (.scc) and numerous subtitle files (.itt).

When I select the subtitle file and have the CC button on then I see the closed captions.

However when I select a subtitle file I won't see any subtitles.

I'm pretty sure that the subtitle files are OK and compressor imports them without any problem.

Question: is it possible to preview subtitles at all or is that just possible for closed captions? Or is it a bug? I really need to check that the subtitles work before I submit to the aggregator and they reject it.