After upgrading from 2015.4 to 2015.5, there is a change in behaviour of the keyword box in Library module.
When you have entered keywords and press Ctrl/Cmd+RightArrow to move to the next photo, in the previous version the focus would remain in the keyword box so you can keep adding keywords. In 2015.5 the focus is lost and you need to press Ctrl/Cmd+K to re-focus on the keyword box, slowing down the tagging process.