Looks very much like a client side issue to me. Hard to tell without a full transcript, though. If the problem is as advertised, it should be easily reproduced and additional information collected.
The problem or confusion at the end may have resulted from using automounter... you'd have to check how that is configured.
Bruce
When I get a round tuit I'll see what happens with a 5.2 client and try static mounts instead of automounting. There don't seem to be configurable attribute caching mount options on those systems or I'd definitely try tweaking those too.