This can happen for a variety of reasons but it most often occurs when Javascripting is involved.

They asked the muggers which of the 60 people in the films they considered easy mark or most muggable and which ones they would stay away from.

and now the bed shook, the curtains rattled so, that I could scarce hear the sighs and murmurs, the heaves and pantings that accompanied the action, from the beginning to the end

Alternatively, you can make supertiles that have more than 1 hex/rectangle each to get grouping. 4-6 areas per supertile is probably O.K. Not all areas on supertile need to be the same, but theer should not be more than two different terrains on a supertile.