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This user has earned the Enthusiast badge (visited the site each day for 30 consecutive days) twice.
I have isolated where this can happen, but a simple fix for now is to simply remove all badges that are single award and were awarded more than once. There are forty or so affected badges in the whole system.
If you are affected by this and are unhappy, sorry, we should be allowed to fix bugs.
It's definitely a bug. When accounts are merged and a reputation recalc is done, a badge recalc should be done as well and ineligible/duplicate badges removed. I don't see any good reason why badges should be permanent and irrevokable*.
*Except for programmer laziness, which is only excusable up to a point.
This has to do with two accounts being merged together.