This is an issue for me also. Started with 5.2.2 then persisted with 18.104.22.168, I use the Mobile>Generic for just about everything since this works well for both my D-Link 520s and my Archos players. Had absolutely no problem before 5.2.2. I downgraded to 5.1.x.x and all is well again, just a little slow.
Mine will start off, slowly climb to around 20 fps then slowly work its way back down to 0.00 fps. It happened straight from the DVD, from ISO images and from the Video_TS folder.
I could rip the DVD to a Video_TS folder then use Handbrake to make the AVI but that was the only thing I could use DVDFab for, ripping to a Video_TS folder to use with Handbrake.
Anyone know if there is a fix soon on the horizon or if this is something that is going to take a while?