it's the presence of the VBR header that's causing the gap to appear.

This is an important distinction, and I think we need to get to the bottom of what's actually causing it. I agree, from the descriptions in this thread so far, that it makes it sound like VBR encoding does seem to have something to do with it.

If the simple lack/presence of VBR headers on the file (the SAME FILE) removes/causes playback gaps, one might think of that as a bug in the empeg player software that should be corrected. Does anyone have more data on this?