Test for 'scrollbind' causing an unexpected scroll of one of the windows.
STARTTEST
:so small.vim
:" We don't want the status line to cause problems:
:set laststatus=0
:let g:totalLines = &lines * 20
:let middle = g:totalLines / 2
:wincmd n
:wincmd o
:for i in range(1, g:totalLines)
:    call setline(i, 'LINE ' . i)
:endfor
:exe string(middle)
:normal zt
:normal M
:aboveleft vert new
:for i in range(1, g:totalLines)
:    call setline(i, 'line ' . i)
:endfor
:exe string(middle)
:normal zt
:normal M
:" Execute the following two command at once to reproduce the problem.
:setl scb | wincmd p
:setl scb
:wincmd w
:let topLineLeft = line('w0')
:wincmd p
:let topLineRight = line('w0')
:setl noscrollbind
:wincmd p
:setl noscrollbind
:q!
:%del _
:call setline(1, 'Difference between the top lines (left - right): ' . string(topLineLeft - topLineRight))
:w! test.out
:brewind
ENDTEST

STARTTEST
:qa!
ENDTEST