Same problem here; my config is ga-ma78gm-s2h rev 1.1 F7 bios, and antec fusion 350.
Disable minidisplay plugin in mediaportal configuration AND also set frontview = never in imon.
This may solve your problem, as I used to have exactly the same problem.
I disabled minidisplay plugin and I solved, but now, how do I use my LCD with mediaportal?
Search "MP2imon" that will solve the standby issues, but may possibly introduce remote issues
I found that the new version of minidisplay plugin didn't solve the problem, but i was using imon v7.2 not v7.6
New Zealand