files disappearing from ls on NFS

Hi,

I've updated one of my -current machines this week (previous update was in 
february). Now I see a strange effect (it seems only on NFS mounts): ls or 
even echo * will list only some files (strange enough the first files from 
the normal, alphabetically ordered list). If I change something in the 
directory (delete a file or create a new one) for some time the complete 
listing will appear but after sime time (seconds to a minute or so) again 
only part of the files is listed.

A ktrace on ls /usr/src/lib/libc/gen shows that getdirentries is called 
only once (returning 4096). For a full listing getdirentries is called 5 
times with the last returning 0.

I can still open files that are not listed if I know their name, though.

The NFS server is a Windows 2008 server with an OpenText NFS Server which 
works without problems to all the other FreeBSD machines.

So what could that be?

Regards,
harti