setpos and getpos strange behavior in vim

When I open a file with vim -u NONE and source this code:

   function! F()
              let l:savePos=getpos('.')
                         silent normal! gg  
              call setpos('.',l:savePos)
    endfunction

    autocmd InsertLeave *  call F()

I got a strange behavior when I leave the insert mode. The setposition is sometimes changing and there is like a z- which is executed.

You can see that if the files is greater than your window.

Can you confirm that behavior ?

My vim is 7.4

Answer

Generally, if you want to save and restore cursor position it is better to use winsaveview() as it has a few other useful features.

Your code could be rewritten to

function! F()
    let view = winsaveview()
    silent normal! gg
    call winrestview(view)
endfunction

autocmd InsertLeave * call F()

Additionally, variables inside functions are automatically locally scoped so you don’t need to prefix them with l:.