[ubuntu] Dual display sleep mode dont work on the HDMI display

Helo, I have a mac mini 2011 quad core i7 2.00 Ghz with two display (Dell Utrasharp U2410). I use Ubuntu 14.04 LTS and all the update are done. The first display connected to the display port sleep well. The second display connected to the HDMI dont sleep well. He turn off (that's what i...