Seeing a post about ear infections reminded me about this. My first beagle was highly prone to clots in her ears. I guess it's from flapping those adorable ears of hers, but I think over the course of her lifetime, her little ears were bandaged from operations 8 times. My second beagle never had that issue. Was this a rarity for the first, or did I just luck out the second time?
beagles flap their ears because of the presence of mites or there might be the start of an infection in ear. Tick bites or mosquito bites can also cause a beagle to flap its ears. Whatever may be the exact cause, a hematoma should best be examined by the vet.
I don't think it is that common, although some dogs are more prone to it than others. Perhaps it was just that way for her. It does seem that once a dog has it, they are more likely to continue having this.