I have a 43" Pioneer Elite PRO-920 plasma. I experienced the exact same problem you are talking about and posted about it on these forums a while back:

[Link: remotecentral.com]

Unfortunately, I never solved the problem, and eventually decided to remove the discrete on command from my MX-850 altogether. To tell you the truth, I never tried any of the newer codes that are available now. For all I know, the bug has been fixed, but since you seem to be having the same issue, I suspect the problem lies in the TV's firmware. I'd be really interested to know if you figure out a solution.