I think you are asking for problems with the vapor barrier there. The surround is (at least in theory) waterproof, then you have another layer sandwiching the drywall. Anything that might have gotten in there had no way to dry out.
Greenboard is no longer approved (at least in the national codes) for use in damp areas, primarily because it really doesn't work well. Yes, the paper covering is more water resistent than 'normal' drywall, but once you put all those fastener holes in it, it doesn't really buy you much of anything. There are some panels that are decent, though. Some surrounds are designed to attach to the studs, and no wall is required behind them. Verify which type you have.