When you kill the corrosive creeper, instead of showing a bloodstain (or whatever the plant equivalent is) it shows the piety icon. This disappears after you step on the icon. Screenshot:
http://i.imgur.com/JQOzh.jpgWhen mousing over plants, the experience bar suggests that you will get enough experience to gain a level.
Maybe a bug, maybe not: Taurog punishes you for converting his items even after switching to a different god and desecrating Taurog's alter.