Dual Monitors don't turn off/sleep when they should

Question

Details:

• Dual 25" monitors connected to HP Envy via HDMI and display port via DVI adapter.
• Power scheme is set up in high performance (Dim Display: Never - Turn Off Display: 15 mins - Computer Sleep: Never)
• Screensaver is set up to kick in after 10 mins of idle (which happens)
• 5 minutes later, the screensaver stops. The "Monitor Going to Sleep" notice appears on screen and monitors go to sleep briefly. All is well thus far.
• Suddenly, the Windows 7 alert sound when a device is unplugged is heard.
• Monitors then turn back on. Screens are black. Only the mouse cursor is displayed. Backlighting is back on.

This only started happening after I obtained and connected the second 25" monitor a few days ago. However, I had a 24" in its place before, and this wasn't happening.

Why is this happening and how do I correct this behavior?

Thanks in advance.

EDIT

Doing a bit more research on the issue I find that the culprit could be the DVI/Minidisplay port adapter as described below found on the AMD site (the computer is using their eyefinity multidisplay tech to run the dual monitors):

What's the difference between active DisplayPort dongles and passive DisplayPort dongles? Passive dongles use the DisplayPort connection to receive non-DP signaling from the connector and they 'passively' adjust the signals to be compliant with the connected monitor. Passive dongles are considered legacy connections, not DisplayPort connections, therefore they do not fulfill the DisplayPort connection requirement mentioned previously and cannot be used to enable 3 or more displays. They do, however, offer an affordable solution to adapt legacy displays to DisplayPort connections. Active dongles use true DisplayPort signaling to 'actively' translate and re-transmit the signals as the required outputs. Because they use the true DisplayPort signaling, they are considered a DisplayPort connection and meet the requirements to enable 3 or more displays. DisplayPort to DL-DVI dongles require an external power supply which is usually through a separate USB connection (the USB connection must meet the USB 'high power' specification).

Could this be the answer?

Answer 1

Solved this problem. Apparently the issue was that the mini displayport to DVI adapter was not the "active" variety, but a passive kind. This caused a failure in communication between the monitor and the computer making the computer think that the monitor was being unplugged when it went to sleep due to electric incompatibilities between the two formats, as accurately pointed out by Shinrai.

Purchasing an AMD/Eyefinity-approved adapter at Frys for $30 solved the problem and now both screens sleep and wake up as they should.