Mine did when I tried to use my Jawbone to make a call. It was very hard to select other cards and I could not use the onscreen key pad. If it happens again, I'll try and be more specific. I have had my Pre2 for only a few days.
Found this, tried it and it worked:
Clean the screen really, really (but gently) well!
Turns out a layer of dust or oil fools the sensors into thinking your cheek is approaching and your pre helpfully hides the screen to prevent unintended touches!