Extra lines of code:

ve.ce.Surface.prototype.onDocumentKeyDown = function ( e ) {
+    ve.log( 'main' + document.getElementsByClassName( 've-ce-documentNode' )[0].innerHTML );
+    setTimeout( function () { ve.log( 'post' + document.getElementsByClassName( 've-ce-documentNode' )[0].innerHTML ); }, 0 );

Test output on holding down 'x':

main<h1 class="ve-ce-branchNode" style="">x</h1><span class="ve-ce-branchNode" style="display: none;"></span>
ve.debug.js (line 33)
post<h1 class="ve-ce-branchNode" style="">xx</h1><span class="ve-ce-branchNode" style="display: none;"></span>
ve.debug.js (line 33)
main<h1 class="ve-ce-branchNode" style="">xx</h1><span class="ve-ce-branchNode" style="display: none;"></span>
ve.debug.js (line 33)
post<h1 class="ve-ce-branchNode" style="">xxx</h1><span class="ve-ce-branchNode" style="display: none;"></span>
ve.debug.js (line 33)
main<h1 class="ve-ce-branchNode" style="">xxx</h1><span class="ve-ce-branchNode" style="display: none;"></span>
ve.debug.js (line 33)
post<h1 class="ve-ce-branchNode" style="">xxxx</h1><span class="ve-ce-branchNode" style="display: none;"></span>
ve.debug.js (line 33)
main<h1 class="ve-ce-branchNode" style="">xxxx</h1><span class="ve-ce-branchNode" style="display: none;"></span>
ve.debug.js (line 33)
main<h1 class="ve-ce-branchNode" style="">xxxxx</h1><span class="ve-ce-branchNode" style="display: none;"></span>
ve.debug.js (line 33)
post<h1 class="ve-ce-branchNode" style="">xxxxxx</h1><span class="ve-ce-branchNode" style="display: none;"></span>
ve.debug.js (line 33)
post<h1 class="ve-ce-branchNode" style="">xxxxxx</h1><p class="ve-ce-branchNode" style="background-color: rgb(246, 246, 246);">x</p><span class="ve-ce-branchNode" style="display: none;"></span>