Phill,
That was very informative. Went back and read and looked at your experience. Haven't checked yet, but since it is raining this weekend I will see what the problem is. I have a feeling it is my tank bag moving forward and pinching the vent tube, which I replaced about a year ago with a non-ducati tube. As for non-vented tanks, the Coleman fuel I leave in my little garage has buckled in the can similar to your tank. One can has almost no unbent surfaces on it, a real indication of what weather variations can do to volatile substances.
Cheers again for the info and glad you got a replacement fairly cheap:roll:

Well, checked the tube and it was pinching. The original black tube became cracked and I changed it for a clear tube. However, the wall strength does not seem to be high enough and it pinches right at the tank tube when I use a tank bag. This will be a cheap fix!! Cheers.