Interesting, wonder what WU defines as 'non-standard characters' - non alpha-numerics? Anecdotally I would have said we have had cases of WU passwords needing to be enclosed in quotes for WU uploads to work, which implies the passwords had non-alpha-numerics in them. One (weewx-user) post I was just reading seemed to indicate that a user's password contained a comma and enclosing it in quotes fixed the issue.
I guess we can always invoke the Weather Underground Uncertainty Principle - if it's WU and it's supposed to do x, chances are it will do x and sometimes y and z and/or anything but x.
Gary