We do have some other options enabled, so perhaps adding 43 & 60 tipped things over...
We did wonder if bootp works differently from dhcp, and may just have been receiving all of the additional lease info... Ive had to remove these options for now, and come up with a workaround.. Its nothing major, its just forced my hand a little to complete the migration. Just at first, we didnt think anything of it, as I had first enabled these options over a month ago, and we have only just started seeing these issues. Leases usually expire after a d ay or 2, so we would have expected this to happen sooner, however, all of these printers do have reservations, so perhaps this invokes a longer waiting time.
What I did notice when I started this, was that I tried to change option 43 at the root/global level, but it wouldnt accept an IP address, only about 4 digits, so I had to manually configure these options per scope.