Can I suggest that you ask this question in Microsoft.public.security?

I'm interested in the answer myself--I suspect it relates to the workings of
the protected store which caches these passwords on the local machine--and I
agree--this ought to work better.  It seems to me that there's a better
chance someone on that group will understand this issue better than we do
here.

(and an equally good chance you'll get no responses, I'm afraid!)