Product review (2 stars): I figured out why they tilt.
Well, I figured out why the burner tilts, as mentioned in the other reviews. One of the three arms is about 1/4" shorter than the rest. This means that it doesn't reach all the way to the edge of the drip tray, and comes to rest just a little bit lower than the other arms.

I wish I thought this was a manufacturer's defect, but I believe it is a deliberate design to make sure that the burner "fits". (After all, a little too small might go unnoticed. A little too big wouldn't.) For this reason I am undecided about whether to send it back-- I mean, what are the chances the next one won't have the same problem?

The burner is not completely unusable. A heavy enough pot (or one with a rough bottom) will stay put. But an aluminum frying pan will fry unevenly because it keeps drifting to one side.