I don't know if anyone else has noticed this yet, but if you convert lower field first video (DV) to DVD MPEG-2 with the default DVD template in TMPGEnc XPress the field order will automatically be changed to upper field first.

CCE does this too, and ProCoder can be configured to do the same thing, but TMPGEnc XPress does it differently. CCE and ProCoder will do a line shift to reverse the field dominance, but TMPGEnc actually separates the fields, drops the first field of the video, and weaves the remaining fields back together.

This can be done with Avisynth also, like this:

separatefields().trim(1,0).weave()

or

doubleweave().selectodd()

There's nothing wrong with this method, but if you want to avoid dropping the first field when your source is BFF, you'll have to create a custom DVD template with BFF MPEG-2 output. AFAIK this only happens with TMPGEnc XPress, not with TMPGEnc Plus.