Sprite Geometry gaining massive triangle counts, why? How to stop?

I’ve been importing sprites, as I thought was the way to do it, and building them up, when I noticed my triangle count getting into absurd numbers.

I checked the wireframes, and found this, on dozens of formerly simple rectangle sprites.

How do I stop this happening, and revert those that have changed back to simple rects?

Situation Dire.

Please help: