Here is a little speculation....
There are only four PWS in about a four-mile radius of me listed on WU. When I first put my station on WU and searched by zip, someone else's station was default. I later "tweaked" my lat/long position (stopped hiding) and suddenly, MY station was the default. When I looked at the WU's google-map center-cross after the zip search, my station was geographically closer to it. A couple of days ago, the "other" station was default again, but I also noticed that at the time, my WL software was down (CWOP issue) so WU may not have had as "fresh" of data from mine, and went with the other unit.
Total speculation, but maybe you and the other station are competing for the "freshest data prize."