After working with Pagerman I suspect there is a setting in WD that is in conflict with rain settings. With Brian out it’s going to be harder to find the culprit.
If you have time could you try using the 2wd.txt to create a minimal WD setup, just enough to get data from the Tempest and see if it records rainfall? This should rule out any left over settings from previous installs or mis-configured entries in WD.
http://discourse.weather-watch.com/t/10889 describes how to do this. This is non-invasive and will not alter your current data.