5324 & NetBIOS over TCP/IP

I understand that the 5324 is a layer 2 device and, if things are working at the
Ethernet level, should be transparent to layers 3 and up. We are trying to
integrate a new 5324 into our network. We have two 5012's at opposite ends
of the office, connected by fiber. At one end, we have a 5324 connected by
fiber to the 5012. Most machines are on the 5324, but some, including one
which is both the PDC & browse master (has IsDomainMaster set TRUE), are on
the 5012 at this end. (All Windows boxes on this network are NT4SP6a.) On
the 5012 at the other end are, among others, two machines which both are BDCs
and have IsDomainMaster=FALSE & MaintainServerList=Yes. As far as I know, all
other computers have MaintainServerList=No and the Computer Browser service
disabled. We are doing NetBIOS over TCP/IP.

As described above, everything seems to work fine. But when we move the PDC
to the 5324 (and we power-cycle both switches & restart the PDC), NetBIOS
browsing seems to go awry. Doing "net view" on the PDC shows only 3 hosts
besides itself, and we have not yet discovered what is special about those
hosts, but they are among those connected to the 5324. Also, the "net view" takes
about a minute to complete, when normally it comes right back. Further,
pinging by name a host at the other end of the office takes almost a minute,
but does succeed, whereas pinging by name a machine on the 5324 responds
normally. However, pinging a host at the other end by number comes right
back, even though the names of both the "distant" and the "near" computers
are in the NetBIOS cache on the PDC. Doing "net view" from other computers
on the 5324 behaves normally, including browsing the resources on the PDC.

Also, the NetBIOS cache on the PDC, in the problem configuration, contains
only "<00> UNIQUE" entries, but after putting the PDC back on the 5012 and
getting back to a working state, it contains other entries, such as GROUP,
etc.

What are we missing? Thanks.