
I did once have a cat that always trimmed his own hind-claws, and did a very neat job of it too!
I don't know what to suggest, except that it may have simply become habit and might have no underlying cause at all. As long as he isn't making them bleed then I don't know I'd be too worried, really. Have you asked his breeder if this is something s/he has noticed in his family?
I suppose you could train him out of it if you don't find any reason - could it be linked to stress and/or anxiety? Fur-chewing and self-mutilation in other animals is usually stress related and often runs in families.
I trimmed my dog's dew claw a tiny bit too short once (he wriggled) and made it bleed - initially I was just going to bathe it and leave it but he licked it constantly which kept it bleeding, so I wrapped a clean tissue around it and bandaged with Vetwrap. In the morning I took off the dressing and could see it had stopped bleeding almost instantly after the dressing was applied and there was no harm done. If he has made them sore, or you are worried he's obsessing about them, then perhaps you could do something similar?