Why does VimResized get triggered 4 times per resize

[Marius Roets]

Hi everybody,
Can somebody explain the following behaviour to me. In my .vimrc I put
the following:
" ------START ----------
function ResizeEvent()
  let &lines = &lines - 1
  execute '!echo "resizing "'.&lines . ' >> test.txt'
endfunction

autocmd VimResized * call ResizeEvent()
" -------- END -----------
Now for every resize event, I get 4 lines in test.txt. The result is
that I end up with 'lines' being decreased 4 times, instead of just
once.

Thanks
Marius