Bad can? Take it back to SW and explain. Might be to late if you put a ton of extender in it already.

So, christophern, you don't think the humid outside weather would cause this?

Not inside with the ac on.
I am assuming the poster is painting inside, maybe I am reading it all wrong

No, you are correct, he is painting inside. But, I think that outside humidity affects the humidity levels inside. One of the cans of paint had been used previously, so we know it isn't the paint, in that can at least.

Pro classic is inherently hard to work with( personally,I do not use it anymore) but if it was OK, then all of a sudden not OK,then you got me.

Original poster here--it was not happening with just a new can of paint--it was happening with the bottom of one can of paint and with a brand new can, too. I find that I can get good results with ProClassic only when using a ton of extender. It works pretty easily on thin trim pieces, but you have to be so careful with doors, and the only way is to take the doors completely off, lay them flat, use a ton of extender (till the paint is almost like water) and then use A LOT of paint so when you come back to feather through it is still wet enough to not streak and clump. Even still you can't get a perfect job.

Well today I am painting the front of an exterior door, and they recommended I used All Surface Enamel. It is a revelation how much easier this stuff is to work with! It still dries pretty quickly, but you can actually pull your brush through more than twice before it ruins the paint job. I wish I would have started using this long ago, it would have literally saved hours and hours of work and turned out much better results.

I have no earthly idea how anyone can possibly use ProClassic straight from the can successfully on any surface larger than a couple inches wide or long.

Oh and I have been using a really good Corona Excalibur brush, so that's not the problem.

I'm certainly not a paint expert, but wanted to chime in about my similar experience with ProClassic. I am DIY painting all 72 of our kitchen cabs, drawers, pantry, and desk area. Tried the ProClassic on the recommendation of a friend (hesitantly, as I'm a staunch Ben Moore fan) and because the color was a perfect match for the new granite. Using a Corona brush, a ton of extender, and the best technique I could muster, I could not get the finish I wanted. Midway through, I switched to BM satin impervo. What a difference! Much easier to work with, much better finish. Wish I'd gone that route in the first place. I know there are ProClassic fans here, but I would not hesitate to junk the stuff and try another product.

Just quit dumping in the extender, there is most likely no reason for it.

Christopern, if I don't dump in tons of extender, the ProClassic is absolutely unusable except maybe on very small pieces of trim in which you don't need to feather out any of the brush strokes.

I tried to use the last of my ProClassic I had in my last can today to paint the pull down attic door. It is only about 3 feet long and 2 feet wide, and even with a ton of extender, I couldn't even go back and feather out the strokes and it was already streaking horribly. That's it for ProClassic with me!!!!!

I don't overwork the paint, but how can you not have brushstrokes and "start and stop" points if you can't pull your brush lightly through the length of what you are painting after applying the paint to the entire surface? It's easier to glop on enough paint to keep it wet when it is something you can lay down horizontally, but obviously you can't take down an attic door.

I don't know what to tell you. I don't have any problem with it

I have only used it once, and had great success. I will admit, it looked terrible going on - brush marks, etc - but it "leveled" out nicely. I had heard about this, but just could not believe how it corrected itself.