I’ve been having this problem since 10.0, hoping it would be fixed. If I do multiple mp3 exports, the bit rate increases each time I activate the mixdown window. For instance, if I set it at 128kbs, then the next time I export a mixdown during the session, it jumps to the next bitrate, i.e.192kbs. It will keep doing this until it hits 320. You don’t even have to mixdown, just opening, closing, and opening the mixdown window causes it to happen. I thought I was going crazy there for a little while until I figured out what was happening.
I suggest don’t use Steinberg’s MP3 export - use a 3rd party program like dBpoweramp, it’s alot better.
Not always convenient, but thanks.