Canon 580EX firing full power in M (1/1 - 1/16) - Fine otherwise (?)

So i just discovered that my 580EX (Ver 1) seems to fire in full power when powered anywhere within 1/1 - 1/16, but when set to lower than that (1/32 .7 - 1/128) it outputs the correct power (checked with Sekonic light meter). Works fine in ETTL - What gives? Is this a defect or did I mess up some hidden settings?

I looked and the Cfn look fine. Anyone has any ideas about this one?

Probable failure of the power control circuit for manual power selection.

So I guess nothing I can do as a user to set right?

Someone else on POTN had a similar power control issue...they sent it in and Canon replaced a defective circuit.

I had a problem in slave mode where one would always fire at full power. Was temporary and may not be the same thing. Another person here with similar experience suggested it was the pins shorting in the hot/cold shoe. Seems plausible, so you may want to check for that.

Thanks guys. I think its a power circuit issue, as Wilt pointed out, as this happens regardless of being mounted on the camera, wireless trigger, ettl wireless trigger or unmounted flash via test button. I think I will live with it for a while as I have a 550EX and this problem is limited only to certain power settings in manual mode. Thanks for taking out time to reply though.