That is an intended feature now. Simply hit C and right click on the passive buff of your pet I think. Very frustration.
My daughter plays a sorc (she is 8), she likes to run around and play with the pets, etc. Now they disappear at times and she can't resummons them by simply clicking their button twice like she used to.
I don't know, maybe people were complaining about accidentally unsummoning their pets during combat or something?