I read through the forums, and sorry if i missed it, but i didn't see anyone with QUITE this issue. My MFD (the moving map that is coupled to the FMS) seems to be skipping, or lagging may be a better way to say it.
I was flying towards a waypoint, but my aircraft wasn't moving on the map, and the distance and time to waypoint wasn't changing. The only way I knew how far away i actually was, was using the FSX map.
Then when I was literally on top of the waypoint, the map suddenly skipped me forward about 80 nm instantly, to my correct position. This of course threw off all the suggested descent paths, and made life moderately difficult for a while.
This has happened a few times, and I am pretty sure that sometimes the FMC lags out as well as the PROG page seems to freeze and won't change the DTG numbers.
(venting start) This product has been fairly exasperating on account of problems like this (venting over)