This is just speculation, but I wonder if the problem may be due to multiple devices (e.g. bridges and USB consoles) being registered under one account and the algorithm draws data from the the wrong sources.
You have to select which sensor to use in MBW, although I guess it is slightly possible that they have a bug in the sensor selection code.
Another thing I wonder about is if it could result from an improper latitude/longitude setting. Once I saw a person who was complaining that the forecast indicated the wrong time of day in the forecast (e.g. showing moon/stars instead of sun, or something like that). The problem turned out to be their longitude setting. (Even though the time-zone was properly set, it was using longitude to determine forecast time-of-day.)
Mine has the correct lat/long defined, as well as the geographic region. Positive for the latitude, negative for the longitude since we are west of Greenwich.
Funny thing is that I just logged into MBW to check the above, and my -30% humidity setting finally made it stop raining! Partly cloudy/cloudy/cloudy, 4%, 15%, 42%. The 1055 is strangely also forecasting PC/PC/PC, 6%, 16%, 31% now with no adjustments. It is 100% sunny outside, and the NWS forecast is still 0% PoP through Sunday night.....