Single step debug not working when PLL running

[sjones]

I am using a PIC18F66J50. It is running from a 4MHz external crystal and after boot up I enable the 48MHz PLL and then run from that with no problem. However if I try and single step after the PLL has started the pic crashes and the program counter goes to $FFFF. The debugger seems to thinks the MCU is always running at 4MHz (Measured on reset?)

[eskimobob]

I've seen strange behaviour like this recently too and as it happens, I was using the PLL (different PIC though).

I was able to find the problem without the debugger fortunately so I did not investigate the cause too closely.