I've had thick mud get all packed into the space inside the rim where it surrounds the front wheel mount/mechanism. I'm betting you had ice formed in there. See here-
http://www.tractorbynet.com/forums/kubota-owning-operating/128900-news-weird-bx24-makes-balls.html
http://www.tractorbynet.com/forums/kubota-owning-operating/128900-news-weird-bx24-makes-balls.html