[Leica] M6 question

[marshall mundheim <mundheim@is.nyu.edu>]

Hello, LUG -- I've been lurking for a few weeks and have a naive question,
one lacking the volatile emotional content of the Red Dot, the Pebble Beach
tree, or P. Di.
        Have just upgraded from my trusty IIIf to a brand new M6 with used
"last non-ASPH" 35/f2, and conversion ring for my LTM 50 and 90mm lenses.
(Keeping the IIIf, too, as I love using it).
        Today I was trying out the hot shoe and found that the flash fires
when the shutter is depressed without having advanced the film, i.e. when
the light meter won't go on.  The flash fires apparently normally when the
film has been advanced, too, but it seems odd that it will flash when the
shutter can not activate, triggered only by depressing the impotent shutter
button.
        Is this normal?  And, if merely depressing the button (without the
shutter moving) fires the flash, how can the flash "know" exactly when to go
off when the shutter really moves?
        I appeal to the obviously expert talents of the LUGGERS to enighten me.
                                TIA,
                                Marshall
PS:  What means "CLA"?