1. Go to https://test.wikipedia.org/wiki/Special:Preferences#mw-prefsection-gadgets and disable all gadgets except one which is loaded by ResourceLoader (e.g. "ShortDiff"), then save your changes
2. Clear you browser cache and local storage
3. Go to https://test.wikipedia.org/wiki/Special:BlankPage and take note of the list of gadget modules in the store:

$.grep( Object.keys( mw.loader.store.items ), function( m ){
    return m.indexOf( 'ext.gadget' ) !== -1; }
).join( '\n' )

In my case, this returned:

ext.gadget.ShortDiff@1347062400

4. Go back to https://test.wikipedia.org/wiki/Special:Preferences#mw-prefsection-gadgets and disable that gadget, and save your changes
5. Check the list of modules in the storage again.
   • Expected result: The module of the gadget should be removed from local storage
   • Actual result: The module is still there, taking space

See Also: T66721: mw.loader.store should not occupy all of localStorage