heres a new one i hadn't seen until i took a short ride. my speedo on the 02' 500 i just got has the needle stuck between 7 to 15 mph sitting still and then when i had it up to around 30 to 40 i looked down to see the needle going backwards towards the 60 mph side.
oh, and no i haven't even taking a look or had it aprt. just thought it was strange lol.

 

That's a new one for me too.

 

Had em stuck at a certain speed before,but the cure was to go faster than the speed showing and it would reset,But haven't encountered one like you say?? Try disconnecting speedo for a couple minutes,hook back up and from a dead start top it out on a straight road and stop and see what happens OPT