I normally use a 4k7 or 10k for pull up's.
It sounds like to me a noise issue with out see the drawing or code, what voltage are the stepper motors running from ?
I had a simular issue with a project that I did where it just randomly operated on its own causing it to start lifting, at first I thought it was a code issue rather than hardware but after some investigation it was related to a noise issue as the buttons where on a long lead which was picking up interface/noise with electrical stuff been turned on/off causing a spike and activating the function. Basicly the cable was acting as a big antenna. I cured this by placing an input filter on the button circuit and carried out loads of testing and the fault did not recur and it has under gone CE testing.
I'll try and post the circuit tomorrow as I'm on my I-pad and drawing is on PC