Kirk,
Have been chatting with Bob about this issue and I can find no consistant method to get 100% data between the two programs. The larger offender appears to be LR, at least it does not always display the new or appended metadata from PM.
At one point, LR did automatically "see" changed metadata and I was prompted with a dialog box asking if I wanted to use the metadata from another program. Alas, this process has completely disappeared (I have no idea why) and I have to manually select LR>Metadata>XMP>Import. This will force an update and loads some of the data, some of the time. It seems to be an generational effect, the more one goes back and forth, the more LR seems to get stuck on one generation of data. In LightRoom prefs I have "Automatically write changes to xmp" enabled.
I am over my head here, but I have spent considerable time with this back and forth and there seems to be some kind of "bug" in either LR or PM that prevents 100% compatability.
Thought you might like to know. Mac OS 10.4.8
Russ