Trailer brake keeps sticking

I've already done a lot of what Old Biscuit is describing. I have verified that I have the correct assembly on the correct side. It is a right hand assembly on the right hand side of trailer. When I push the magnet one direction, the opposite shoe expands out and releases when I release the magnet. When I push the magnet the opposite direction the other shoe expands, but does not fully release when I let go of the magnet. Instead of the shoe just expanding out, it goes out and up at the top and just sticks there when I let go of the magnet. I then have to take a hammer and very lightly tap it and it goes back into position. I imagine when the drum is in place, it would prevent this upward movement at the top. I hope this makes sense. Any suggestions?