The search box in the top-right has a search suggestions box that includes a "More" button when there are more than a certain number of suggestions. If a user clicks on this button, the focus on the search input box is lost.
Version: unspecified
Severity: normal
https://gerrit.wikimedia.org/r/#/c/54638/ should fix this. However, if you click "more" you will instantly hover one of the added suggestions as long as you do not move the cursor away fast enough. There are quite some more improvements that could be made. However, at some point, the entity selector should feature a more sophisticated paging mechanism anyhow.