(I noticed this bug on projects, but it may occur in other places you can enter multiple complete-able items into a textbox.)
I wanted to enter a bunch of people to a new project. So I went to https://phabricator.khanacademy.org/project/members/45/, and in the "Add members" textbox started to type a username. The completion popped up, and I hit tab to accept it, which worked fine.
What I expected to happen next is that the input box would retain the focus, with the cursor right after the name that was just entered.
What actually happened is the focus went somewhere else (to the window root?) and I had to re-click in the textbox to start entering my next name. Not the end of the world, but annoying.