Need to update to the latest patch but I didn't see a fix for this in the change logs.

The tactical regeneration spell has an occasional tendency to 'infect' squares on the World map with its visual, leaving the sparkly green shimmer behind upon departure of the unit bearing the active spell. This seems to happen most often for squares where some kind of encounter occurs.

Another, related example of this contagious visual is in the store. See below. Apparently the Shop Keeper got a bit too close to my sovereign and had some of the green stuff rub off on her.

"So is that a regeneration spell you have active or are you just excited to see me?"