Doubling Gmail Contact Groups?

Now that I've been using Gmail for a while, I generally love it; but I've encountered a persistent, annoying issue with contact groups and wonder whether someone has tamed it.

Basically, my contacts' displayed groups frequently double:

If I select affected contacts and "remove" their duplicate groups, they return to displaying their groups normally - for a while. Within a day or two, they – though I'm not positive the exact same contacts are involved – return to doubly displaying their groups. Frankly, this doubling affects more of my contacts than not.

Any ideas, Gmailers?