I looked at some of my multi-format ebooks from FictionWise. The PRC version is sometimes in the old PalmDOC format, which only has the title in the header. In such cases Windows MobiPocket Reader also fails to pick up the author. Even when the PRC version is in READMOBI format, it might not include the author in its metadata. Sometimes the "Kindle Compatible (MOBI)" version is identical to the PRC version, but in other cases it is different and typically better (more metadata and a cover image). In the cases I tried, Calibre 0.4.76 picked up the same metadata as Windows MobiPocket Reader - which means that the Author is often Unknown. I only tried about half a dozen titles, so this wasn't a definitive test.
In one case, the PRC (PalmDOC) file had no metadata but it did have a copy of (some of) the original .opf file which shows up in Windows MobiPocket Reader as "eBook Info" under Contents. Interestingly, Windows MobiPocket Reader did not extract the Author from eBook Info, and still shows the author as Unknown, but FBReader did detect the internal metadata and correctly identified the author.