There's been a few threads about this but in light of the duplicate bug thread rule I think it's worth bringing to light again.

The mouse hole object in the map editor cannot be placed in front of a ground even if the hole is foreground and the ground is background. This bug came about due to a update a long time ago and map crew was told it would be fixed 'next week'. It broke a lot of maps, so I feel it's worth looking into again.

At the moment, the best a mapmaker can do is attempt to draw a hole where it should be using color joints.

If they fix it, I say they should make the foreground option make the hole go above the grounds, but under the mice. It would be awkward being behind a hole.