I don't know, wether it is a bug or a feature. If you are updating with multiple protocols, postscript is called one time for every protocol.
This could cause heavy problems, if the script is running more than once at the same time.
I have attached a patch that make the postscript run only one time. Parameter is a list of updated IPs, separated by spaces, just like before, but I have eliminated duplicated IPs.
Perhaps you find this useful.
PS: I'm just working on a shellscript for updating zonefiles, if anyone is interested.