Steps to reproduce the problem:

1. Open http://www.amazon.com/ (or another slowly-loading page with an
input field).
2. Switch to another tab.
3. Start typing an address in the Location field.
4. When the search input field shows on the Amazon tab, keyboard focus
moves to that field. Now everything I type is typed in the Search field on
the invisible tab.

I think that keyboard focus should never get lost because of a page loading
in the background. If the user types an address, they probably want to
finish it, even if another page gets finally loaded.

Now I noticed: Keyboard focus is also lost when a page is loaded in the
middle of bug typing :) But this time the input doesn't show in the Search
field (or anywhere else).