Why did this suddenly start is my question too. At least it seems sudden. It used to be her habit to lick the block a bit after breakfast, but not spend the day there.
I think I'll call and ~ask~ the vet if he has any particular concern.... and then look for the loose mineral supplement at the feed store when we go.
My first guess as to why would be boredom. I've also noticed when there is a weather change (Hasn't it been raining there alot?) that horses will suddenly start doing strange things, eating the barn down, eating the bark off trees, etc. I've had horses that didn't ever do things like that suddenly start, so it may not be anything serious.
Becky