The 145's had a similiar problem in the early days when I was an engineer at BRAL, the flap transmission units were recommended to be dry, IE no lube, what happened was condensation formed and when the aircraft was at altitude the condensation froze, on descent the flaps wouldn't operate, we managed to get them to change there way of thinking and introduced lubrication in the units, the problem stopped, maybe it is something similair on the 170/190's?