Not sure is the best forum for this...
I've been search these forums to try to understand the use of my speedlite (actuallz a Metz 48 AF-1) on my .
I did not under the behavior when I was in AF/Tv or M modes. I was getting the impression that ettl did not work in these modes, as it seem that the flash existence was been ignored.
I could not find anything here, but I googled may way to this link: http://photonotes.org/articles/eos-flash/
A good tutorial on the back development of ettl-II, and explains my misunderstanding.
Basically in these modes, camera is the ambient (before the flash) to bring up the background, and the ttl stuff kicks in for the foreground. Auto/P modes meters with the flash, probably leaving you with a black back ground.
Anyway, the tutorial in quite good, sometimes a bit technical, some bits out of date and centric but I believe useful for all flash users.