I'm having the same issue. Started about the same time as mentioned above. I'm using the latest version on my Mac at home iTunes 10.5.3(3) 64 bit. I upgraded to test out iTunes Match,... I wanted see if I could listen to my music at work . So upgrading to the latest version of iTunes and turning on iTunes Match are the changes I've made recently. I also believe the SD versions want to download at work ?! I'll have to double check that.
I opened a ticket with support. This is what I finally got from them:
On the computer, in iTunes select Store, and choose to Sign in.
Once you are signed in, in the left hand side of iTunes, select on the iTunes Store. Afterwards, on the right hand side, select Purchased. Under Purchased choose TV shows, and select all TV seasons, or anything to view the video you want to watch.
Once you have the video up, at the bottom left corner of iTunes application, you should see a check box that has a check in it, and says Download to HD When Available. Remove this check. This will allow you to download the SD version of the video.
After following these steps, if you still have any issues, please let me know.
I replied asking them when this property was introduced because I know I have never visited that purchased page and I had never checked the "Download to HD When Available" checkbox but they completely ignored my question. I have to assume that they introduced a new property and defaulted that property to true. Basically they introduced a behavior change. From reading comments on different discussion boards I imagine this behavior change was welcomed by most...just a few of us who still have old devices and need that SD (or just like the SD because it looks fine and doesn't take up as much space).
I hope following these instructions helps you also but if not then I would open a formal ticket with support.
I assume that Apple has made this change to where HD copies download instead of the SD copies because people buying the HD version of a show, want to watch the HD version because HD is why they are buying it.
Personally, I went through and deleted all SD copies of my shows over the last several years because I had no use for them.I buy HD versions for the HD version.
Thanks for the input folks. I'll try this as soon as I get home. In my family, we have 2 Apple laptops (15 inch and 13 inch), 2 iPads, 2 iPhones and an iPod Touch. None of those devices are going to benefit from HD video playback ? I buy the HD versions for watching on HDTVs via AppleTV where you can see the difference and because you ALSO get the SD version for your mobile devices - though I do watch the HD version on my laptop (only because it's already there). For the mobile devices, I only transfer the SD versions, so those versions not auto downloading was starting to concern me. Hopefully Moore's Law catches up to these solid state drives. Some iDevices have been stuck on 64 Gb of SSD for a while. At 1 Gb+ per 40-45 minute TV show, you can chew up space fast on a 64 Gb iPodT/iPhone/iPad (especially if you have (HD) apps/games and other data). And hopefully that doesn't double the price.
Thanks again for the help !