Funny than that I can't see the flash in "Manual 2" then. My flash is the old non-alpha YS110, maybe it has to do with the problems of those, bugger. (Anyone here who can confirm this problem?)
Checking Heinrichweikamp - 450D and 50D (and thus probably 500D) are listed at sending one pre-flash with a 50ms delay
Hello Oskar,
I have a 500D and YS 110a strobe. I link them together using a FO cable. The 500D does pre-flash but not because of the reason we ordinarily think camera's pre-flash. It pre-flashes to discover the output of the camera's flash which is governed by Canon's E-TTL-II technology. (this, E-TTL-II, cannot be disabled )
With my camera, 500D and my strobe, 110a, the strobe will fire and in synch with the shutter when the 110a is set in Manual I. And when it is set in (DS-)TTL. In both instances the 'slave' switch is set to ON.
The switches on these two strobes can feel 'kinda spongie' (for lack of a better description), verses the nice solid feeling magic-click-like feel with other switches we've known to come and love. When I use mine, I make sure that the switch(s) are in the position they need to be. Because if they are not, 'right there', the strobe will missfire or not all. You could try that, double checking your switch positions. IF that doesn't help-
Some people I know have had problems with the 110 model strobe, such as you have. I'd contact Sea and Sea's service and their facility located in California. See what they can do for you.
Larry