I recently (within the last 2 months) painted part of an interior wall
a dark red color. Whenever you rub a finger or hand against the paint,
it leaves a whitish mark. The mark wipes away easily with a damp
cloth. But what is it, and what is causing it?

The details:

- The wall is sheetrock.
- I used two coats of Behr flat latex paint. No primer. The room had
already been painted with a latex paint.
- Because I was sampling the color to see if I wanted to use it for
the whole room, and was in a hurry to see the end result, I painted
the second coat before the first was completely dry. Could that be a
factor?
- The paint itself does not seem to be rubbing off, either on the
finger that rubs the wall, or on the damp cloth that rubs the mark
away.
- This does not seem like chalking to me. There is no chalky surface
on the paint.

Any thoughts?

Thanks
Tracy