Joining two like AVI XVID/MP3 files gives me a final file that has half of its audio (first half) is ok and the second half being off just a bit.

Gspot shows the same stats for each of the files with the exception of the A/V Interleave being 60ms (IMRR 0.99)
and on the second file the A/V Interleave is 61ms (IMRR 1.00).

Are these differences the problem?
and is this an actual encoding issue or is it just a field in the header information of the AVI files?

Thanks...