I've noticed the same problem with our '07 Bambi SE, and it seems to be related to the screen door "dragging", or catching on the abrasive door strip at the bottom of the doorway. You can tell if this is happening by separating the screen door from the main door, and closing it to see if it binds up on the bottom of the screen door. I haven't taken it in yet, but I'm wondering if a few minutes with an angle grinder on the bottom edge of the screen door might help.
"I have found through trial and error that I work best under duress. In fact, I work only under duress." -Ed Abbey
Jerry & Susan
2007 19' Bambi SE; 2010 Ford F-150 5.4L SuperCrew 4x4 w/ FlipPac camper shell