For some odd reason I'm not able to delete Webstorage (Using the old sync. plugin) with the "Clear Storage" action.
My guess is that the website is blocking the process so that it doesn't work correctly.
Please note that I'm able to use the plugin as a data storage, I'm just not able to clear stored data.
@Tom or Ashley whoever is working on the Arcade currently, please investigate this bug as soon as possible.
Edit: I do not create a bug report because it is working fine on other platforms, so this is a platform specific bug.