How to eliminate $-> from php words

using vim huge version with GTK2 GUI on ubuntu 10.04

I mean to eliminate the following characters:

'$' , '-', and '>' (ascii 36,45,62)
from php word syntax.

Neither
:setlocal iskeyword-=$->
as an ex command nor
autocmd BufRead,BufNewFile *.php setlocal iskeyword-=$->
in .vimrc
has the effects that I am looking for.

to test my efforts I invoke : set iskeyword and see the
following
:iskeyword=38,42,43,45,47-58,60-62,64-90,97-122,_,&
where ascii 45 and 62 are still present.

What am I doing wrong?
thanks
--
Tim
tim at johnsons-web.com or akwebsoft.com
http://www.akwebsoft.com

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