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 Canon.

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 metering the ambient light (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Anyway, the tutorial in quite good, sometimes a bit technical, some bits out of date and Canon centric but I believe useful for all flash users.