they get excited when ridden!Its not just Ducati, Triumph, Aprilia and a few more were effected by tank swell. I believe Acerbis was the manufacture of the tanks. When I had my Duc, I started to watch the tank slowly swell and touching my steering dampener more then 1/4in swell in a few months... Sold that sucker right away... If I had the S 2011 + year when they put aluminum tanks on, I would of kept it.... I believe on the ducs, whether it be a monster, 1x98, 848 07-12 have the tank issues.... Ducati solved the problem by replacing swelling tank with smaller plastic tanks, that still swell... haha
this is just a fast google search of Ducati tank swell
http://www.ducati.org/forums/1098-1198/55508-1198s-tank-swelling-again.html
http://www.ducati.org/forums/1098-1198/44118-expanding-gas-tank.html
http://www.advrider.com/forums/showthread.php?t=945640