I saw one (a White treadle) where the little screw on the front right hand corner (that holds the machine down when you don't want to flip it up and look under it) was not in the locked position when it was folded down and the machine flopped open and wedged itself into the cabinet. It was a 2 contortionist job to get it to open.

And yet one more style of lift mechanism: leather! DS's aunt's treadle is a...NewHome Climax, and the lift "chain" is a strip of leather.