Shift-Tab to move keyboard focus results in two highlighted apps

When using tab to move around the app center (either its front page or the updates page) the current app has a grey box while pressing tab repeatedly moves the focus between the widgets of the currently selected app (changelog icon and the right-hand button).
When the button has keyboard focus, pressing tab moves the grey box to the next app. So far so good.

However, going backwards using shift-tab does not remove the grey box from the current item even though the keyboard focus moves to the previous item's buttons. This results in the state shown in the screenshot:

The fonts app was highlighted, I pressed shift-tab and app above (maps) was highlighted as well. The keyboard focus is on the "open" button of the maps app. I have never used the mouse on that screen. The App Center was launched via keyboard shortcuts and I've moved around the interface using only the keyboard.