- Open the VisualEditor
- Put the cursor in a place where "Paragraph" (or whatever else) disappears. (For example, into the ugly and unbearable empty line in pages with infobox at the very beginning.) The content editor must be kept active and cursor blinking.
- Scroll it down a bit.
- Press Ctrl, Alt, or Shift, or every possible combination of these
- See the content editor scroll up step by step (or as many steps per time as many keys are in combination.
I can reproduce this in Chrome 29.0.1547.57 and Firefox 23.0.1 on Windows.