Dell U2415, auto rotate?

[TridenT]

Got hooked up both my monitors. The Dell U2415 won't auto rotate. It doesn't matter which is set as my primary display. The U2413 auto rotates like a beast and works flawless every time. The U2415 won't auto rotate at all.

Is it just the way the monitor is? Does it not include auto rotation functionality?

I thought it did but it's not working at all. My search engine queries are failing me. Thoughts?