Displayport 1.2 to 1.1 no extended desktop

MSI R9 390 (latest crimson drivers), Dell U2415 (DP 1.2 enabled), Dell U2412M (DP 1.1)
Using the mini DP cable that came with the 2415. Using a standard DP cable between the two.

I choose extended desktop using the WinKey/P shortcut, but it doesn't stick. Is it the standard cable between the two monitors? The 1.2 to 1.1?
I can't seem to get anything other than a duplicated desktop, which is of no use to me. I need the extended desktop. What am I misiing?

Hi I not really following what your trying to do. are you connecting one monitor to the other monitor with a cable? or do you have separate cables going from computer to each monitor?

Hi. Thanks for the response. I was having trouble getting two monitors to display in extended desktop mode even though settings on the R9 were correct and I chose Extended Desktop via the Win 7 Winkey +P shortcut. Getting into windows Screen Resolution settings sorted it out (right-click desktop, choose Screen Resolution). Turns out it wasn't taking the shortcut option for some reason. All is well now. Thanks.

ok thanks for letting us know how it was resolved

Thanks for your willingness to help. :)