Assembled a simple steam engine and then created 2D drawing of the complete engine. Asked for a cross section and it worked well. Then I decided I wanted three shafts to not be sectioned. Changed number one...OK. Changed number two...not OK. 2/3rds of the cross hatching on the cylinder and piston disappeared. OK, allow the shafts to be sectioned again. Did not clear up the problem. Removed the cylinder and piston from the assembly and reinstalled them (when are we ever going to be able to easily replace parts in an assembly?). Re-opened the 2D drawing. No joy, the partial cross hatch appears to be stuck there permanently.