Its healthy and perfectly normal!! Due to the rabbits diet, and its digestive system, it is not able to process all the nutirents out of the food first time round so they produce a 'first' poo which is very soft, squishy and smells like cabbage. They then reinjest this and then produce the 'second' poo which is the one you will see in the litter tray.
A rabbit which does not reinjest 'first' poos may well be a poorly rabbit, and is at risk of fly strike (very nasty). If your bunny is not eating these it maybe worth taking to the vet, or having a look at bunny diet and giving it hay only for a few days in case bunny has a bit of a poorly tummy.