Can you detail what the settings need to be in PM5 prefs in order for this to work?
Well, essentially you want PM 5 to read/write XMP sidecar files for TIFF-based RAW files and embed XMP for JPEGs, TIFFs, PSDs, and DNGs.
You need to get your color class label names to match in both applications and that's about it. You don't want to synchronize the IPTC Urgency with the Color Class since Adobe's software won't enforce that restriction.
But no matter your PM 5 settings, you have to get LR to update its internal database with the changes you make to the files with Photo Mechanic. That's where LR's Metadata menu comes into play.
-Kirk
-Kirk