I have been painting for almost thirty years and two rules may be helpful:
(1) While you MAY, in individual cases, get good results without following all the manf's instructions, if you do much painting, you WILL have times when the instructions were INDESPENSIBLE to obtaining good results - If you want to improve your odds, follow the instructions- this directed at all of you who DON't properly kill mildew or otherwise prime walls; and
(2) Virtually all paint brands at some point sell A FEW gallons of paint with problems. I recently started applying Behr Ripe Currant eggshell enamel on properly prepared walls in dried-in, climatized conditions. The paint streaked, clumped, and ran. The first rule when this happens - close the can, stabilize your brushes and take it back. Unless the store employs an atypical idiot, they take it back. The Behr salesman took it back, and I continued on with the replacement Behr paint, which gave the expected good performance. Total loss: 40 minutes of my time for painting plus 20 min travel time. Not desireable, but definately NOT earth-shattering, either. (I have had problems with Glidden, Monarch, Sherwin Williams, Dutch Boy, and Walmart over the years. None of these problems indicated that the company was a "Bad manufacturer" and all of the sellers took them back - in all but one case, they did so graciously. These problems are ofset by a better than 98% success rate with all these brands.) Good luck with your future painting.