Chainsaws

I just purchased the Poulan Pro PP5020AV chainsaw on Saturday 8/17/13. If you need the serial number I can provide. My problem is starting difficulties. It starts cold without a problem following the directions in the owner's manual. It starts hot without a problem. If I use the saw for 1/2 hr to 1 hr and then go eat or take a break, when I come back 20 minutes later it is very difficult to start. I took it to the local service center as I was instructed and they were unable to reproduce the problem. I brought it home today and used it again and found the same problem. I use the saw for 1/2 hr to 1 hr, go eat dinner, come back and I can't get it started again. I tried every choke/lack of choke/primer bulb combination. Pull the choke all the way out, push it back in to set high idle and still nothing. No indication of flooding. Eventually for some unknown reason it starts and runs again after about 25min of pulling. Sorry for the lengthy explanation. Please advise. P.S. This is the second saw I got from the Menard's on Sat. The first one had exactly the same problem and they were kind enough to exchange. The second one that I still have possession of is the one in question.