I've been seeing various issues with feedburner and iTunes lately. iTunes basically uses the feed we expose over feedburner to provide you the episodes. For some reason the feed seems to be cut off on the iTunes side after about 30 entries. This seems to happen only occasionally.
Furthermore Feedburner seems to have had some hickups lately, I've been missing the enclosure tags within the generated xml, seems to be working right now though.
You might be on the safe side if you don't subscirbe to the feed via iTunes music store but direclty via the RSS feed:
To do so head over to podcasts menu in iTunes, remove the old subscription and use "Extended -> Subscribe to a Podcast" with the url above. Not sure if the menu is named that exact way, I'm running the german version of iTunes.