Sorry to hear about your problems.
As far as the issue with the reversing of the playback direction of an audio clip goes, this seems to only happen under very specific circumstances. It was reported by a few users since the release of this current product generation, but never with a reliable description to replicate the problem here. At one point, we thought we had replicated it here, but when it actually came to the analysis and fixing of the problem, this turned out to be a pretty elusive issue once again. :-( So, if you can provide the necessary details and enable use to reliably produce the problem, we'll gladly give it another go. Thanks.
As far as the second, bigger problem goes, I'm not really clear on the current status of that issue. If that issue was somehow specific to that project, because of something you had done with the use of track volume curves, and you had already sorted out this issue somewhere along the line and successfully mixed down the project to MP3, then how did this problem return? Does it still affect the same project now when doing further work on it and trying to export again? Or did you manage to replicate it on another project, also by using track volume curves? I'm not sure I can follow that. If you can reliably replicate this issue, I'd be happy to hear more details. In the meantime, I'll also fiddle around with track volume curves and exports to see whether I can make the problem happen.