NFS sharing: folders disappear/reappear at random

[tonster]

I just recently purchased a TS5810D and everything seems to be setup properly and went pretty smoothly, however I'm noticing that over NFS folders just randomly disappear and then reappear.  I'll do an ls and a bunch of stuff will report permission denied, and then another ls immediately afterwards and everything is fine. Has anyone else seen this or are there some tuning parameters I'm missing? 

Here's what I see:

[root@docker1 dir1]# ls /dir1/share
ls: cannot access '/dir1/share/dir': Permission denied
ls: cannot access '/dir1/share/dir2': Permission denied
ls: cannot access '/dir1/share/dir3': Permission denied
ls: cannot access '/dir1/share/dir4': Permission denied

Immediately after that, doing an ls /dir1/share and everything is listed.