Steps to replicate the issue (include links if applicable):
Type in the Lookup box, then delete all the characters.
What happens?:
On typing the box becomes animated, when you delete all the characters the animation stays.
What should have happened instead?:
On the box being empty again, the animation should disappear.
Software version (skip for WMF-hosted wikis like Wikipedia):
Other information (browser name/version, screenshots, etc.):
Example of bug in action in Wikifunctions: https://phabricator.wikimedia.org/T312115.