Description of Bug: Cinna's used caltrops are continuing to trigger. She placed a stack of two caltrops which presumably disappeared when walked over- however the tile no longer has visible caltrops and is continuing to trigger the effect.

Reproduction Steps:

1.  Placed two caltrops on same tile
2.  A critter walked over them 
3.  Caltrop disappeared 
4. Critter walks over tile where trap previously was 
5. Caltrop effect triggers 

Error message (if applicable):
Screenshots:

https://i.postimg.cc/D0H3HgDf/location.png

(Location is Sessha's burrow)