The search field, categories, & font family/size cannot be focused when changing focus with the tab key. Oddly enough, it can be focused with shift+tab to cycle focus backward. Using just the tab key, focus goes from the 'To Clipboard' button to the character grid, skipping the upper controls.
That's a regression, probably caused by a bug fixed in Qt. See bug 246806 comment #1 how to focus the search field.
Can no longer reproduce this bug; closing