mp3 export doesn't show correct file size til another export done

[obidon]

When I export a region as file to mp3 it appears on the audio drive much larger than it really is until I export another one.

This one too appears larger but the first one then self corrects to show real file size. I'm using 128 kps and it only happens in slow (hi quality) mode, not in fast mode.

I've searched this forum numerous ways and can't find any reference to this. Doesn't happen in itunes (although I can't choose quality modes there without using variable bit rate, which I can't use in the PT mp3 add on, so not a fair comparison.

PT8 on both leopard and snow leopard. Mac Pro quad core