Grooming with a mouth full of poop...why?!

I have a question about something weird (and gross and annoying) Bramble does all the time. He'll reach down as if he's eating cecotrophs, groom his underbelly, then spit out a piece of poop that's now all crumbled and broken up right on the floor. He makes a big pile of these squished poops normally about half a foot away from his litterbox. They aren't cecotrophs, they're really crumbly and light in colour which is his normal poop. He has all these poop crumbs on his pretty white belly from this habit. Why would he be doing this?? It's not new, I've noticed he's done it for at least a year, but the half-a-foot-away from the box has been happening the past month or two.

Bramble is neutered, 3 years old, eats 1/4 cup of timothy pellets a day and tons of hay. He's 4 pounds and is recently bonded (less than a month ago which I think accounts for some of his poor litterbox habits).

I've never heard of this behaviour. Any insight?

So if I understand correctly, he is reaching down and getting his normal dry poos and chewing them up and making a pile of crumbs of them. If so, that is very strange behaviour and I've never seen any of my rabbits do that. I wonder if its just a habit he has because he wants something to nibble on while he is on the toilet- maybe moving a hay holder or putting a handful of hay in front of him would distract him from doing it.