These two appear to be appear to be somewhat related glitches:

1) A statue sitting on the pressure plate, to no effect. Maybe these need to be constructed out of heavier materials.

2) Depressing the pressure plate with a dramatic pose, despite it not having anything on top of it.

Both of these occur when you place the statue down on the pressure plate as normal, then try to pick the statue up while standing on the left edge of where the gate is expected to come up. The first time you try to pick it up, the statue remains in its position, but the button (and, as a result, the gate) pops up again (#1). Attempting to pick it up a second time causes the pressure plate to depress and get stuck (lowering the gate), but lets you pick the statue up normally. At this point you can throw the statue around however you'd like, and the plate will remain pressed down until something moves/is placed onto it again.

Odd variation that I found. Not sure how this came about.