Ford Focus wipers operate with ignition turned off

I was outside the car with the ignition key. The wiper switch was in OFF position. I noticed the front wipers working, slowly. The problem occurred several times today, both with car locked and unlocked. The wipers seem to operate a few sweeps and then stop. I've disconnected the battery. I'll need to connect the battery tomorrow, but was planning to take out the wiper's fuse until I can sort out the problem. We had a frost last night and the wipers blades were stuck to the windscreen so I know they did not operate overnight. I did not use the wipers today until they were unfrozen, so that could not be the cause..