it just takes because it needs to recalculate your bells total from the post. it doesn't actually penalize you for editing
if you make the post shorter you lose bells, but if you make it longer you gain bells. and if the length stays the same, your bells do as well
confirmation from Tina over here:
http://www.belltreeforums.com/showt...read-Bonuses&p=6646302&viewfull=1#post6646302
also, the post of mine above her's, which proves this in action