Problem
In the List Lookup control, it's possible to type text into the control to filter the results. When a result is selected, the search term remains in the control. This only occurs on List Lookup controls with the 'Allow multiple values' option enabled on New Responsive Forms in Office 365.
Solution
The search term is automatically deleted when a user clicks, or tabs, outside of the control. This is a known behavior with no work around to prevent it. However, this behavior carries no functional consequences.