Tabbing eventually lets the user see the invisible content
I have a complex border layout with a card panel in the center region. The contentEl for the card is set to some generic html that loads with the page. A user loads a panel into the card panel. The problem comes about if a user presses Tab too many times and essentially the focus goes from the currently active card to the hidden content.
To demonstrate this problem, I have created an example page that you can drop into the ext examples folder. Just extract it, load it, and hold down the 'Tab' key.