I opened 3 chests for 1 med hydra lamp and 2 small hydra lamps, instead upon claiming the rewards i got a normal medium lamp and 2 prismatic stars......huh?
RNG giveth, RNG taketh, but mostly taketh.
Same thing is happening with Clairvoyance. I've wasted so many keys blocking unwanted chests in the colour I've chosen only to be given an unwanted prize in a different colour, generally white.