I've shot a couple more rolls and haven't had the problem I've described, but the mirror will still stick occasionally. Turning the speed dial a few times will release it.
Check the foam damper on the forward lip of the top of the mirror box has not deteriorated to the point where it can cause the mirror to stick to it. Replacement foam can be obtained on eBay and it is very good stuff.
.::Gary Rowan Higgins
A comfort zone is a wonderful place. But nothing ever grows there.