My glass shrimps are eatling one of my mollys alive!!!?

I have a 60l tank 3 mollys, 2 glass shrimp and 2 dwarf guramis. When one of my mollys ( always the same one) goes near the bottem of the tank the shrimps grab hold of its tail and start eating it. Her poor tail fin looks a rigt mess. I currently have the molly in question trapped in the tank so the shrimps cant get to it.

Please help i cant understand it. i was told shrimps are peacefull. could it be possible the mollys tail had dies or somthing and thats why they are eating it.