Qt Creator needs restart to recognize manually added syntax highlight definitions

When opening file for which syntax definition is missing Qt Creator suggests to update syntax definitions (which trigger download of out-of-date files), however, if you manually add appropriate syntax definition to the User Highlight Definitions Files folder, it won't recognize them until its restarted, prompting to Update Syntax Definitions again and again.
Ideally, Qt Creator, when Update Syntax Definitions is triggered should check for updates in both the default syntax def repository and local folder.