This may be old news, but I just noticed this gem the other day. Not exactly Kindle 1984 quality, but disturbing none-the-less.
Leo LaPorte recently discontinued his AAC version of TWIT. Not a big deal. The other day I noticed that its listing was missing from the podcast section of my iTunes library, when I hadn't remembered unsubscribing.
Apparently (best guess) iTunes must have removed the podcasts from my library when it was removed from the iTMS, even though I still had unlistened to episodes remaining. I actually wasn't sure about this until I found that all the episodes still exist in iTunes Music folder in the Finder.
I can't say I'm a fan. There's no reason why I wouldn't want to keep episodes of a podcast after its been discontinued.