This user has earned the Enthusiast badge (visited the site each day for 30 consecutive days) twice.
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.