Sort "Specify IP Address" by age of use
The assign IP address option in the OnApp user interface may offer an IP address at the top of the list which was just unassigned by another customer only 5 minutes earlier. OnApp doesn't seem to take into account if other IP addresses have never been used or if other IP addresses have been unassigned much longer.
Instead, the Specify IP Address list should be sorted in reverse by age of last use. The IP addresses that have never been used should always appear at the top of the list. If all IP addresses in the available pool have been used at least once, then the one that has been sitting unused the longest should always appear at the top off the list.