Yeah it is strange. I think any individual miners mining Karma at this point pretty much know what they are mining and intend to keep at least most of their rewards. Those are so small anyway that the big dumps can't come from them, they have too much volume.

I have two theories, both might be wrong.
1. They are multipools dumping to convert to BTC. Karma is currently among the most profitable scrypt coins after all. Has anybody watched the net hashrate closely to see if there's a lot of fluctuations (pools hopping on and off)?
2. It is a whale that is not satisfied yet. Maybe he/they have "only" 2-3 billion coins, but want 5-10. They use their stash to drive/keep price down and accumulate more Karma.

There's also the possibility that a whale wants to exit his position, but usually such a move is preceded by a small pump and/or fake buywalls. I don't see either.

One thing I did notice on Mintpal is that sometimes these dumps seem to happen almost in "retaliation" for people driving price up. Every couple of days someone would start buying up Karm and raise price by a few lit. Shortly after that there was always a pretty big dump that pretty much tore through any walls put up. If nobody buys for a while the dumps are smaller and less frequent. One thing is for sure. Whoever keeps dumping their coins is watching the markets closely...