Bug: Missing metadata in PSD (but not PSB)

On a very small number of PSD files, the metadata is missing. This is quite annoying and I never realize it until late in my workflow when I am looking at JPG output and realize that the metadata, especially the © information, is not there. Tracing backwards is how I discovered that it is there for the raw (NEF) but not in the PSD.  A really freaky thing I also discovered is that on one PSD file, I saved it as a PSB file (because I realized it was going to be large) and that has the metadata but the originating PSD file does not. Huh?  This is a very small number of files, so I suspect it will be hard to track down the root cause.