Double scroll bars

I changed the height of my editor to 900px and when the content is longer than that i get 2 scroll bars (example) a bit of poking around in firebug and the following css seems to fix the issue:

.CodeMirror-scrollbar {
  overflow: hidden;
  position: absolute;
  right: 0;
  top: 0;
  z-index: 5;
}

<div class="CodeMirror-scrollbar" style="display: block; height: 901px;"><div class="CodeMirror-scrollbar-inner" style="height: 1120.2px;"></div></div>

However are there any unintended problems or is there a better fix for the double scroll bars?

http://ww.wp.xz.cn/extend/plugins/wp-editor/