Hi, they sound like malformed caecotrophs to me, does he do normal droppings as well? Malformed caecotrophs do tend to look like mini cowpats I must admit! We should call them bunny pats
It tends to indicate quite bad caecal dysbiosis, which although not immediately dangerous, can lead to health problems as firstly bunny should be consuming these caectrophs - which may explain the weight loss (as they get a lot of nutrition from them) and if they smell wrong and are full of too much of one sort of bacteria bunny will discard them, which is why you are finding them instead of them being eaten. If they are coming out malformed then the caecum really isn't doing it's job properly. The other problem is that long-term caecal dysbiosis can predispose your bun to stasis as when the bacteria are out of control this can trigger an episode of ileus and stasis as there is a lot of interdependency throughout a rabbit's gut.
Caecal dysbiosis basically means 'the bacteria in the caecum are out of balance'. I'm not very good at explaining it but the caecum is a very important part of a rabbit's digestion as a hind-gut digestor and it contains beneficial and not so beneficial bacteria that act on the smaller food particles in a rabbit's diet. When things go wrong the bad bacteria outweigh the good and you get dysbiosis. It's all dependent on the amount of starch (sugar) bunny is ingesting and gut motility affects how well the caecum works which is why a high fibre diet (lots of hay) is so important, not only for motility of the intestines, but for balance of the caecum as well.
This is a great article that explains it better than me!
http://www.veterinarypartner.com/Content.plx?P=A&A=670&S=5
http://www.bio.miami.edu/hare/poop.html
A vet check up is definitely a good idea, sometimes discarded caecotrophs can be a sign of dental issues.