Wein HS slave + Canon 550 = problem

I am using the Canon 550 flash on the Wein HS slave set to Manual mode and
used as my fill light.

In "Manual mode", I make a test fire so that I can get the exposure using a
flash meter.
The second time I test fire nothing happens when I press the button.
The only way I can seem to "reset" the flash is to turn it off then back on.

I have tried the above procedure with the Wein HS slave covered.
Doing this, I am able to get repeated test fires from the flash.

All custom functions on the flash are off.
Ambient light falling on the slave is 1/30 f/4 at 400iso.
No back light flash used.
Main light is f/8 and everything (main, fill, subject) is within 10 feet of
each other.

It apprears to me the the slave has fooled the flash or visa versa.

Anyone have any ideas or experiences with this?
-Mark