The solution is actually simpler than you'd expect, and the problem shouldn't arise again once you've taken care of the existing events. If you head to Admin > Event Schedule, edit the offending events, and at the bottom, just check the boxes next to the roles. Then save. Your roles should re-appear.
As far as I know, all the issues with this have been resolved (with the exception of the
changing absentee bug, which I'm working on right now).
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It's all in the reflexes.