Question about input redirection in -c

[Stefan Dalibor <dalibor@immd3.informatik.uni-erlangen.de>]

Hi,

from the manpage:

  -c   If -c  is  present,  commands  are  executed  from  the
       immediately  following argument.  Any further arguments
       to rc are placed in $*.

and:

  exec [arg ...]
       Replaces rc with the given command.  If the  exec  con-
       tains  only redirections, then these redirections apply
       to the current shell and the shell does not exit.   For
       example,

            exec >[2] err.out

       places further output to standard  error  in  the  file
       err.out.

this made me think

  rc -c 'pwd; . /dev/tty'

would have the same effect as 

  rc -c 'pwd; exec </dev/tty'

But it has not - the first command behaves as expected (execute pwd,
then read from the terminal), the second executes pwd, but the input
redirection is ignored and rc exits.
Browsing through the source code revealed that the redirection *is*
done (doredirs() is called in exec()), but is ignored in doit() after
returning from walk() - the EOF the lexer got from parsing the
argument string `overrides' the input redirection because no pushfd()
is performed. 

A comment in doit() (`` "last" can be clobbered during a walk() '')
and comparisons with other shells indicate that rc does this on 
purpose - but I can't see the reason for it. For me it's puzzling that
`exec</dev/tty' changes its meaning when executed via `rc -c', so
could some kind soul please explain it?

Bye,
Stefan

--                                                                  --
Stefan Dalibor                dalibor@immd3.informatik.uni-erlangen.de