Thanks Jarod.

You should be using mceusb. lirc_mceusb is dead and gone. Both Fedora
and Ubuntu's 0.8.7 packages are (or at least, should be) for userspace
only, and both are patched to work with the in-kernel IR drivers. The
difference is that Ubuntu hasn't kept up with fixing the in-kernel IR
drivers in their kernel.

Do the changes that have been made to the kernel drivers affect the delivery of pulse/space signals from mceusb to lircd? The problem I'm trying to solve (as I see it) is that the Fedora system sends a 'gap' value at the start of a packet, and a 'ptrail' value at the end, while the Ubuntu system sends a 'header' value at the start of a packet and a 'ptrail' then 'gap' value at the end. Is it likely that changes to the kernel driver have affected this?