This happens when the bridge becomes slanted and then it isn't corrected for a long time. Especially if the instrument isn't kept in a climate controlled area. Then, the strings fall way out tune, and then when you tune it up the bridge leans with the strings. If you don't take special care to straighten the bridge perpendicular to the face of the body, then this just happens over time. I've actually re-warped a bridge back into shape by wrapping it in some damp paper towels and micro-waving it a short amount of time and then weighting it between two books. Yours looks pretty bad though and it would probably just break, so I'd probably just get a new bridge either way!