Temp file bloat with "Treat Mpeg audio" checked

[nyco_ork]

My capture device usually brings audio in already coded as AC3. However, I just used VideoReDo's new audio adjust settings to increase the volume on a project that had low volume. In making the adjustment, VRD recodes the audio as Mpeg.

Now move to Movie Factory 4. I've finished the project, have Dolby Digital as the audio output. Usually this is a straight passthrough, no problem. But in this case, the Mpeg has to be converted, so I check the "Treat Mpeg audio as non-DVD compliant" in order to force the conversion.

Now I go to the burn screen. Normally the file size for the temp files is the same as the final burn. A 4.1 gig DVD requires 4.1 gig for the temp files. My system partition on the primary HDD has 7.5 gig of space remaining, so it is usually big enough. But with "Treat mpeg" checked, the temp file size doubles, to 8 gig. Why is this? It forces me to use my outboard USB megadrive for the temp files, and that slows the burn down.

Anyone know why the file size is doubled? Is there that much extra processing needed to convert Mpeg audio to Dolby? It should only be reencoding the audio, not the whole project.

RB

(Later edit)
This behavior is even more weird than I originally described. On this last project, I saved it with "Treat Mpeg audio" checked, then closed down. The next day, when I reopened that project, the output file size had doubled again. I had to uncheck "Treat Mpeg," go to the burn screen, empty the temp folders (even though the temp files at this point were on a different HDD), resave it, close the program, and then reopen both the program and the project, before the file size would behave itself. Yet with another project, that had been processed in the same way but was slightly larger, this didn't happen. This part of the behavior is obviously a bug. The part I wrote about above, in my original post, seems to be normal behavior. I'm still wondering why it is normal behavior. If I'm forced to go to the USB 2.0 HDD for MF's temp files, the burn takes 40% longer than it does when I can use the internal HDD.