I get this to a small degree. I think its to do with static electriciy and there is more than one technique that might help. One technique is to dispense the grounds into a cup and stir it with a toothpick or similar. I just tap the pf on the bench a couple of times during dosing. The clumps seem to break up and it helps to ensure the grounds are more evenly distributed.
I used to thwack slowly at first but now I do it a bit faster. Dont know if that helps the clumping.