There's a certain momentum in PHP TextInputWidgets, SearchInputWidgets when clicking on Indicator- and LabelElements sometimes make focus visually disappear.
Example showing behaviour in Chrome 55/Mac (not visible on single-line TextInput on demo for me, but on multiline and core's singleline)
URL used in example: https://en.wikipedia.org/wiki/Special:BotPasswords
Expected result: Focus should remain on input.