I am going to try to do what the dealer suggested with this new chain, cut from the bar closer to where it meets the body of the saw, and see if that helps. If it doesn't, I am going to ask them to give me a different saw. I don't know if I have a lemon, or if this particular saw is just not very good at the particular application. I may upgrade to something else.
When the dealer told me that this happens to anyone cutting what I am cutting, I told them that, while I like this saw better than the poulan, the poulan never once had a bent chain in the entire year I used it. They didn't have a response to that.
I should also point out that their response was not just from one guy, but from the sales guy, one of the owners and the mechanic. They were all curious about my issue, and seemed to have lots of experience with this kind of problem. They have a contract with the local city trimming department, and said that when they cut buckthorn, they use this saw, and they have the same kind of problems with the chain--it goes with the territory. I have no reason to disbelieve them, they've been very good to me in every other respect, so I didnt' get the feeling they were just trying to get me out the door.
On the other hand, I can't say I feel like I've really gotten anywhere with this issue. I would be inclined to say I am doing something wrong, but the dealer looked things over and confirmed that I am using the machine properly, including how I've been putting it back together. I also rechecked the manual for the chain and the saw to make sure the chain and bar are a match--they are. I have a feeling that the guide links in the chain are just not very strong. When I suggested using a stronger chain, the dealer basically said that will make things worse. What do I know. Like I said, I just know this didn't happen with my other saw, ever.
I plan to use the saw as suggested later this week. If the chain bends again as quickly as it has in the past (seems pretty likely), I plan to take the saw back to the dealer and either ask for something else, or get a refund. Even if this is "just what happens" when cutting buckthorn, the saw is mostly worthless to me in that case because that is 90% of the reason I bought it.