I will certainly give that a shot.
Another sort-of-related issue. I'm beginning to feel that my 5DM2 and my 430EX don't like each other too much. I was shooting manual mode indoors over the weekend with 430EX mounted on body bounced off ceiling. Realizing that I need more flash power I added FEC on the flash gun from the previous setting (when I was using outdoor fill flash) from -1 FEC all the way to +1/3 FEC. I did this in +1/3 increments.
As I went from -(1), to -(2/3), to -(1/3) to (0) I saw what I expected....EVENLY increasing levels of flash output. As soon as I went from 0 to +1/3 it seemed like it jumped by +(1 and 1/3) instead of just by +(1/3). I tried going back and forth again, and the same thing happened.
What the heck is going on here? I will try to post test shots tonight similar to what I did for the OCF shots in my OP.
i dont have a 430 EX or the excellent 5D2, so not a subject matter expert... but what do you mean you were "using outdoor fill flash"?... is that specific exposure mode or white balance mode on either the camera or flash? Or do you simply mean you were using the flash as "fill" instead as flash as primary lighting?
I would again ask the prior question... were you using the flash in ETTL/TTL mode or were you shooting manual flash mode. ( I do realized you noted you had the camera in manual exposure mode 
)
also, if you don't mind me asking, are you already familiar with the flash illumination sequence that the camera goes through once you 1/2 press the shutter, and once you full press the shutter? knowing what the sequence is might aide you in finding if you have a flash problem.... If you're pressing the FEL at anytime, that would be effecting the result as well. Don't mind me asking, since i'm not assuming you DONT know, but as you didn't mention any of that, I'm not sure if you are indeed taking all that into consideration if you you're trying to determine if you're having a speedlight problem.
thanks
m
