During auto-completion, whenever the mouse cursor happens to be in the area of the auto-completion popup, the entry under the mouse cursor is highlighted - even if the mouse has not been moved.
Steps to reproduce
Type [[a (or any other letter) to start auto-completion.
Move mouse cursor over third item of the auto-completion popup.
Hit [Backspace] to abort auto-completion.
Type a (or any other letter) to re-start auto-completion.
Expected result
The first auto-completion entry should be highlighted.