Guys, if anyone is having such problems, send all related files to us for analysis. Since we wrote all of our own codecs, we have 100% control over all of this stuff. I don't want to take for granted that VBR will be unreliable. I'm basically unwilling to make that assumption and also unwilling to jump to any conclusions until we've seen the problem with our own eyes and then had a chance to fix it.
The problem could be entirely and easily solvable, but we always need to see what is happening and then analyze the problem.
Bill