Comment 3 for bug 233803

I can confirm this and add what I think is a related issue.

Create layers 1,2,3 as above, although I tried this with multiply blend mode. Set layers 1 (top) and 3 (bottom) to normal blend mode, then set layer 2 to multiply blend mode, all at 100% opacity.

Create a colored rectangle in layer 3 and one in layer 1, different colors (I use blue and yellow). Select the blue rectangle in layer 1, and SHIFT+PAGEDOWN it twice to layer 3. I notice two issues already: First, it does not assume the multiply blend mode in layer 2, only when it enters layer three does that take effect. Secondly, the boundary box for the rectangle extends way beyond the rectangle (something like a margin is introduced).

Now the blue rectangle does not ever seem to lose the multiply blend effect, regardless of the layer to which you move it. Adjusting the blur on the blue rectangle restores its normal blend mode as well as bounding box.