I can add ten static IP allocations in DHCP without an issue. When I add another, the first entry (with the "lowest" IP) vanishes from list and is replaced by the new one. Next time the "vanished" client aks for a lease it gets a dynamic one and appears in the list with the dynamic allocations. As a result I can't have more than 10 static leases at once.
*** This bug has been marked as a duplicate of bug 12050 ***