PIC 18F45K80 CAN bus speed issue

[lexicon]

I'm using a PIC 18F45K80, running @64MHz (16MHz resonator, 4xPLL), CAN bus is set to 500kbs in Flowcode7.
When I try to use the internal CAN it is not working correctly - it seems the transmit speed is about 10% too fast.
Although PICOscope is able to decode it, our CANalyser does not accept the traffic which results in a permanent re-transmit:

FC7-not_working.jpg (95.39 KiB) Viewed 90930 times

Using the same configuration in FC5 works fine (CANalyser accepts, no re-transmit):

FC5-working.jpg (82.77 KiB) Viewed 90930 times

As can be seen, the FC7 transmit period (delta between cursor positions) is 201uS and in FC5 it is about 218uS.

One solution here would be to use FC5, but that gives me issues with other parts of the project and it would just make sense to be using the later version.

ETA: The same project also uses the UART @250kbs and that appears to be fine, so it's not a general speed issue, it seems to be CAN specific.