As a maintenance electrician I've seen switched neutrals within UL approved appliances many times. It makes you wonder but there isn't a dern thing you can do about it. If you rewire the machine you've voided the UL.
To answer the question ... I only have a "what if": If the current was arching or pulsing to ground at some point near the fuse you may produce heat that is transmitted to the fuse but not necessarily through the fuse. Any signs of arcing or sparking?
