z motors going forward then reverse randomly

ok
sanguinololu 1.3
stepsticks

I hooked up my board and have printed close to 90 hours without changing configuration.
I took my bot somewhere over the weekend and now has this problem.

I get my bot back and hooked up
One motor will be moving one way then change direction

I tried hitting all the pins with my solder iron thinking it might be connection
multimeter says both motors are hooked as expected
Swapped stepsticks
swapped weird motor for x axis and the motor worked as expected''
reflashed firmware

anyone have any suggestions?
thanks
bryan