This is one of the oddest ones I’ve seen — and one of the easiest to reproduce, though it’s not straightforward.

UnitedHealthcare’s consumer website, myuhc.com, changes themes when you’re not expecting it. And all you have to do is click the back button.

Check out these two screenshots:

The first is what appears to be MyUHC’s newest website. The second is what happens when you read one of MyUHC’s articles, then click the back button. The second website looks a lot older, a lot less polished (graphics don’t align, less snazzy), though is apparently still functional.

What’s mysterious is the reproducibility. Earlier today, reproducing the theme change meant navigating to an article, pressing the back button, pressing the forward button once, then pressing the back button again. That was in Firefox. In IE, all I had to do was press the back button once, and the site mysteriously changed its look and content. Now, about six hours later, both Firefox and IE display the same behavior — but only sometimes.

Try it yourself.

First check out their article about swine flu (the first article in the list), then press the back button. If that doesn’t work, press the forward button, then the back button again. If that still doesn’t work, rinse lather repeat. It appears, too, that the only way to get the newer-looking website — and thus, the article about swine flu — back is to clear your cookies. Also, the url on what appears to be every page is “http://www.myuhc.com”. Shouldn’t there be something following the domain name?

Mysterious.

Update, 6/5/09: I found the following text in the “What’s New” section of the old MyUHC website:

New myuhc.com coming soon!

myuhc.com, is going through a complete redesign to better meet your needs. The new site will have enhanced tools and features; quicker and simpler access to these tools, and content that is easier to read and more detailed. Look for your new myuhc.com in June.

I guess they’re not done yet.