fb 1.5.1, fedora core

I have a situation where, sometimes, a database that copied to another
identical machine will only allow 1 connection, any additional attempt
to connect just waits.

exit the first connection and a single waiting connection completes the connect.
I've done this with isql so as to eliminate client/network issues.

Now granted that this is a database that is copied rather than backup,
copy backup file, restore but I've had it happen with a database where
I've done backup, restore on same machine to new name, copy to new
machine. Nobody has connected to the restored database on the original
machine nad it's still had this problem. I can't work out what could
cause this, anyone?