Mechanical altimeters, especially the 57mm Winter are known for being lazy on a fast descend.
It can differ more than 200m compared to ground just at landing after a flight, wait a few minutes and the needle will smoothly be back at zero (or QNH).

The only explanations for a S80 to show different altitude before start and after landing is:
- Its broken (not likely)
- The pressure (QNH) has change during your flight.
I only have the mechanical altimeters as I have to, the flight computer is my primary indicator of height. I guess the majority of XC-pilots use the computer/vario as primary.