Hi
Clients unexpectedly losing connectivity is not something that should be happening.
I'm currently looking at a number of 10.7 and 10.8 Servers. I also have a 10.6 Server which is behaving as expected and has been for the last 4 years.
FWIW none of the OS X Servers (ASIP 7.6, 10.0, 10.1, 10.3, 10.4, 10.5, 10.6, 10.7 and 10.8) I've installed, managed, repaired or serviced over the years have ever displayed the behaviour you describe. Obviously not unless there's been a deeper problem elsewhere. Problems have ranged from simple misconfiguration, permissions, mis-behaving or incompatible 3rd-Party applications or hardware issues/failures.
The other possibilities are the client OS itself has a problem or there's an obscure issue with the network.
HTH?
Tony