I (think I) remember that with previous OS X versions I could have the display turn off while connected to external monitors, but the latter wouldn't be turned off. So, when I would turn the display back on, all the windows would still be in their monitor.
Now, when the display goes off, all external monitors are shut down (?), so all windows are moved to the small mac screen and i have to drag them into position by hand.
Any hint on how to solve this?
I have an early 2015 retina mac book pro and El Capitan installed. My external monitors are Dells. The energy saving preferences already prevent the mac from sleeping when the display is off.