What jes00 is saying is that the fillcan has no client sided code which could break these functions, which are all client sided.
In that perspective he is right.
It seems
highly unlikely that the fillcan breaks these client sided add-ons.
The fact that one other guy has the same problem doesn't mean the problem lies within the fillcan add-on.
Once again, so far only you two seem to have that problem since it works fine with everyone else.
Have you tried a completely clean install of Blockland with the fillcan add-on and enviroment favorites (or any other mod it breaks)?
You should try that.
FALSEEDIT:
I was too slow apparently;
also. in case you were never aware.
the fillcan also has a function in it that makes the entire players avatar turn the selected color and transparent too if the player is sprayed with it. it might have something to do with the avatar stuff messing up
No, this is all server sided and can't break your avatar customization in any way.
TRUEEDIT2:
I've had a problem similar to this before v21. Not sure if it's the fillcan, but if I set my decal as the Blond Hair face, it sets it as the red beard face and visa versa.
I have this problem though i can't seem to find a real pattern.
It certainly doesn't involve the fillcan, since it is even there when you don't have the fillcan enabled as far as i know.