430 ex compatibility with xsi?

hey guys.
i have a 430 ex speedlite and for some reason i can't get the m off in front of the zoom.even when i shoot in av or tv, the zoom on the flash doesn't adjust automatically like it's supposed to. could it be that the xsi isn't compatible with the 430ex flash?

Press the Zoom button on the flash until the "M" disappears. Then you'll be set for auto zoom which will match the focal length set on the lens.

wow. this is the weirdest thing that has ever happened to me.
i've been messing around for like 2 hours trying to get the m to disappear, and it literally just worked. . .

thanks