I too have problems with the % watering not working with the Zimmerman method. I tried clearing browser data, rebooting, etc, etc. I then entered the query from the post above directly into my browser.
http://weather.opensprinkler.com/weather1.py?loc=pws:KCAROSEV19&key=542f5f8759cd342b
after that, the % adjustment changed. Is it possible that once the browser communicated with the weather.opensprinkler.com that it opened a connection that was not previously opened by the firmware in OpenSprinkler, but once opened by the browser the connection worked for the firmware?