CUPS "locking" after first print?

I'm adding an "AirPrint" extension to my enhanced Raspberry Pi image (which already has facilities to allow SSH, VNC servers, FTP, and a Webserver).

It is basically working, the Avahi service permits IoS devices to 'see' the non-Airprint prints as if they are Airprint Printers and I can print the first document after a cups server restart. However, not a second over the network. Local test prints are fine.

Essentially the cups network service seems to 'lock'.

A cups restart clears the problem.

I've used a similar technique on PC Linux without seeing this problem- it seems to be a R Pi issue.

Has anyone on the group been experimenting with this?

(I have Googled this to death BTW).