I also painted over flat latex in test patches, just to try out the colors. First I tried some Sherwin Williams top of the line interior satin. Absolutely no problem. Then, I tried Martha Stewart satin. Shredded and peeled off the wall in 24 hours. Now, it is my understanding that latex over latex (especially over a similiar color) would not require a priming coat. Am I wrong. I know you can prime anything, but in this case is it really necessary? I actually thought the paint was defective and returned it. The better quality (more expensive) paint right next to the Martha paint was perfect. So, I'm just reporting the facts here...!