I have the same issue. I was originally told by my farrier that the flare was due to a mild infection of the hoof (think fungus or white line), then I had a second opinion given yesterday by a barefoot trimmer that is not my current farrier. I'm just going to provide what I was told. I have not done this yet, still confirming the advice, so I can't say if it works. But I was shown a horse he had trimmed a week earlier that had a flare caused by the same reason, and it looked immensely better.
Observation: No infection. Foot is not balanced appropriately, putting extra pressure on outside of hoof wall. This is not coincidence... the flare is occurring because of that pressure, on that side of hoof. Hoof should be leveled out and balanced, not simply trimmed shorter on the same angles. Flare can be trimmed and sanded down to the point of 1/2 the thickness of the outside hoof wall. Rasp the toe to provide a slight roll.
It's a lot like nuts and bolts - if the rider's nuts, the horse bolts! ~Nicholas Evans
Last edited by KarrotKreek; 05-16-2012 at 12:12 PM.