Single Player TestLive.
Place a trebuchet in a location as part of a bases defenses.
This may take several days. I have only been able to see this happening in the Admin Fly mode.
Normally, as i move around the base, I will find that the platforms where they are located are empty. Of the 11 in the base, only five do not explode/implode. After the recent patch, they started disappearing after 7 days.
This was done in my TestLive game. Have not recently checked the Live game.