[lug] Subshell behavior with potato bash?

[socket at peakpeak.com]

Since I upgraded to debian potato a month ago or so, an upgrade of
bash (or perhaps grep) started breaking a declaration in my
.bash_profile.

Here's the relevant line:

f="$(who | grep $(tty | sed s./dev/..))"

I'm currently running:

GNU bash, version 2.03.0(1)-release (i386-pc-linux-gnu)
grep (GNU grep) 2.4
GNU sed version 3.02
who, tty (GNU sh-utils) 2.0

Here's the error:
grep: a: No such file or directory
grep: tty: No such file or directory

I can probably fix this myself if someone could explain just what a $
before () does.  I would assume that it might be the return value of
the subshell, when the subshell finishes, maybe the output of the
subshell... this little quirk doesn't seem easily explainable.

Identical line works fine under bash 2.01.1(1)-release
(i486-pc-linux-gnu) that comes with slink.

Any thoughts?  Thanks!

--
Chris Riddoch                  socket at peakpeak.com
Will provide pseudo-insightful commentary for food
                   http://www.peakpeak.com/~socket

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