Ram bug in hidden trees

Watch this clip:

As you can see, when building a ram in a hidden position makes the forest disappear and, thus, making your units visible and blowing your hidden strategy. I’ve tested it many times, its always the same. Is this supposed to happen?

If not, pls fix

I think it is a mechanic. If you place mangonels in a forest, when they unpack they make the ground become dirt. If you look closely they do that everywhere they set up. Its probably to avoid easy traps using a small army as bait then unleashing a ton of boulders on your enemies. Granted you can still do this using cliffs.