Robert,
1, 2 MHz aren't supported oscillator speeds. From the manual:
There are a limited number of valid numbers that can be used: 3 (3.58MHz), 4, 8, 10, 12, 16, 20, 24, 25, 32, 33, 40, 48, 64. These are the only frequencies for which PBP is able to accurately calibrate its timing.
As for the Saleae LOGIC....Your computer can't keep up due to loading on the USB bus (or too much other stuff going on). Make sure that the LOGIC it's the only device on that USB Host controller. If you don't know, just try another USB port.

But, I don't know what was wrong with me this morning. I was probably thinking in terms of instruction cycles of the PIC.....
If the samplig rate is 4MHz then the shortest resolvable time is of course 250ns and not 1us as I wrote. Even so I'd definitely try to get the sample rate up a notch (or two).

/Henrik.