Anyone who bought recently from a yard and has a dodgy odometer should take it back and:
1. Get it fixed
2. Get the timing belt changed by them (as you cannot be sure of how many kms the car has done).
I had the same thing from day one, odometer would start and stop. Got the seller to do the belts at 68,000kms (supposedly).
I have now added another 100,000kms and changed the timing belt myself since.
Anyhow... be aware that if your odometer is iffy, then you should do the timing belt as soon as possible (for the price of doing this it is great insurance that your engine will not go bang).
El Bee