PIC problem: Touching the crystal capacitor makes the system slows down
I think that maybe that pair of capacitors usually in the 10's of pF are not well chosen. Check the crystal specs. I'd suggest 10, 15 or 22pF but it depends on the crystal and up to some extent to the layout and oscillator circuit. Microchip datasheets also have some advice on oscillator components. Whenever you touch a oscillator circuit with your finger or a probe, you are basically adding a capacitive load which usually dampens the oscillation and stops the clock but some times (it could be your case) make the crystal oscillate into a harmonic frequency. It's not so unusual.