No, in my case, one was even empty. Chest content is random.

http://www.kiya1.de/images/Divdt_Verdpoly1.jpg.html

sorry, this map is a jumble in German/English => Polykiste is Polymorph chest. Here you see both of them marked on the map.

http://www.kiya1.de/images/Div_Polymorph.jpg.html
http://www.kiya1.de/images/Div_Polymorph2.jpg.html

here are the effects - as you see => bunny/frog. Just take care to have a spir. res. of 15, then nothing can happen.
Kiya