multiple frames with same name on (frame-list) - what is the cause?

[Drew Adams]

As far as I know, I am not creating any multiple frames with the same name.
After a sequence of operations such as `iconify-frame',
`make-frame-invisible', and `make-frame-visible', however, I somehow end up
with some frames listed multiple times in `(frame-list)'.  I'm not sure of
the exact sequence of such operations that leads to the problem.

Actually, the "duplicate" frames have the same name, but they are different
frames, as indicated by their hex ids. One of them will have frame-parameter
`(visible . t)', and the others will have frame-parameter `(visible)'.
Again, all of these frames are listed in `(frame-list)'.

These multiple frames are messing things up when I try, for instance, to
iterate over `(frame-list)'.

Anyone have an idea where the multiple frames on `(frame-list)' are coming
from? I don't see anything in the various function definitions or the doc
that would indicate that one of the functions (e.g. `make-frame-visible' or
`make-frame-invisible') would create a new frame instead of operating on an
existing frame (its argument).

BTW, the only way that I'm using `make-frame-visible' is through
`frame-configuration-to-register' followed by `jump-to-register', and these
functions use `current-frame-configuration', which just iterates over
`(frame-list)'.

I see this problem in both Emacs 20.7 and Emacs 21.3.50 (from CVS July
2004).

Thanks,

  Drew