Page Up/Down keys don't behave as expected in the Source mode of the inplace WYSIWYG editor

You can reproduce this easily by:

• editing the Sandbox home page in-place using Chrome (the problem doesn't reproduce with Firefox)
• switching to Source
• trying to use the Page Up/Down keys to move the caret inside the edited content

The page is scrolled, but the caret remains in the same position. If you start typing you don't see where you type... Very confusing.