ASUS PA248Q Not waking from Sleep

I just acquired a used iMac (21.5-inch, Late 2012) and decided to buy a nice PA248Q ASUS monitor to work with the system as a second display. The monitor is connected via TB with a MDP to DP cable which is made by QVC. The Monitor works fine until the Mac puts the displays to sleep. Upon waking the PA248Q gives the "NO SIGNAL ON DISPLAYPORT" message and immediately goes back into power save mode. If you use the soft power on/off switch to cycle the monitor then it is back. This is annoying!

I have seen several posts on Google and the net about this problem as the changeover to Mavericks was happening. This is Yosemite (10.10.3) with all the latest updates and I am hoping there is a good fix for this issue. I do understand that TB is not exactly DP, but is compatible, and I definitely needed to not spend a great amount of money on the Monitor.

Interested if anyone has ever gotten this problem resolved and specifically with this monitor.

I have plans to purchase a new Mac Mini with two of these in the near future, so I am VERY interested in solving the issue.

Thanks in advance for your advice and help.