10.9.3 external display not recognized after sleep

Good to know, but not using either of those here and this occurs.

It's just another 10.9.3 introduced bug along with the Apple logo appearing twice during start up with the clam shell closed during boot up or reboot.

Hello, I am having a similar issue. I see the mouse on each screen, but no picture. I have to go to System Preferences/Displays/Color for them to come back. Nothing else works. I have one connected to the HDMI and another through the Thunderbolt-HDMI. I guess we wait until they fix this.

I just resolved a similar problem, my MacBookPro with lid closed and in sleep would not wake the monitor (even though the laptop would wake).

The solution turned out to be a setting on the monitor. It was auto switching sources to find a live one (HDMI, DVI, HD15) and I guess that when the MBP woke the monitor wasn't looking on the HDMI input. By the time the monitor started looking to that source the MBP had decided no monitor was attached.

Setting the monitor to always use HDMI (no searching / switching) solved it for me.

Thank you for this information. Very helpful. Your information on doing the following resolved the issue of my second monitor not being recognized.

Press Shift + ALT + CMD and then the Power Button. Check the color of the light on the Power Cord, it should change from amber to green and come back to amber.

Then, press: ALT + CMD + R + P + the Power button. With this you are erasing the video cache memory.