Not sure why WD is picking up data for rain rate. With Brian not available the best idea I can come up with is to try the 2wd.txt troubleshooting step to prove or disprove that it’s a misconfigured setting in WD.
The next time you expect rain try using the 2wd.txt to create a minimal WD setup, just enough to get data from the VP2. This should rule out any left over settings from previous installs or mis-configured entries in WD.Installing multiple instances of WD on your computer describes how to do this. This is non-invasive and will not alter your current data.