I was having this problem in sp15, too. When tabbing among form fields, OW has been struggling with radio buttons. WebKit would normally say, tab to one radio button and use the arrow keys to select a different one. However, OW is missing the boat on the first step and ends up tabbing back to main page focus instead of the radio buttons and then,
in my case, tabbing back to the text field I was just in, as if there was nothing else available.
(I'm currently forced to select radio buttons with the mouse and click in the next field before I can return to keyboard speediness.)