Josiah - I read the other post - thanks for the link.
I'm a bit confused, though. The MOthers clay bar is yellow as indicated in your post, but AutoZone doesn't stock it (they stock the Meguiar's bar). The reason I asked about what color the bar was, was to make sure it was a Mothers bar instead of the Meguiar's one, which many folks have had streaking problems with. Both company names start with "M", and they get interchanged all the time by accident.
We have had 3 different version of clay since introducing it - the first was very pliable, the second was a little too plasticy to suit me (sounds like the one you had), and the third was between the previous 2, and a pretty good bar in my opinion. We started shipping the 3rd version about 10 weeks ago.
The comment about the QD streaking sounds directly related to your comment about it drying on the paint - I'd guess it was a darker color, and you indicated you were doing it out in the sun. Try working a smaller area or in the shade. The streaking should be easily removed with more detailer and a good towel.
It's a rare day I hear of our bar leaving streak marks. Usually it's the result of using water as a lube.
I passed the url of your posting on to our chemists.