zsh always resets LINES to 24.

[Jahwan Kim <jahwan@math.lsa.umich.edu>]

Hi all,
    Maybe my post didn't propagated well...
    
    My environment is 31x80 vt-100 (pseudo-)emulator, OSTYPE=solaris2.5.1, and
TERM=vt100.  Of course, the terminfo entry of vt100 specifies that it
has 24 lines.  So in my .zshrc, I detect where I login from, and reset LINES
if I login from home:  export LINES=31.
    Then at the very first prompt, echo $LINES gives me 24.
    
    So I set out to read man pages, faq, and dejanews.  Found out ttyctl
might have something.  Added ttyctl -f in my .zshrc:
export LINES=31; ttyctl -f.  Nope.  ttyctl -f; export LINES=31.  Again
LINES goes back to 24.

    I experimented a bit more.  I typeset LINES read-only.  Well,
surprisingly or not-so-surprisingly, something is always trying to reset
LINES=24.  I get the error message: 
zsh: read-only variable: LINES
after every external commands.  Nowhere in the man page could I found a
explanation  (I typed /LINES in man zshall.) 
	
    What gives?  This is not a correct behaviour, is it?  Am I missing
something obvious?
	    
TIA,
Jahwan