It happens as it gets old, sits too long, and picks up moisture. I've never had a problem with the clumps - I just smash them up. Mine sometimes starts to look like clumpy cat litter as it nears the end of the bottle. A solid mass, as you say, sounds like a lot of work to break up, and is something I would probably return. ...then again shipping for the return might be more than replacing the bottle or dealing with it.