I use Photo Mechanic and Adobe Camera Raw. I convert my RAW files to (locked) DNGs. I then cull these DNGs in Photo Mechanic, and then I edit them in ACR, which creates a sidecar XMP file. If I later star, or color label my DNGs in PM, ACR loses the DNG←→XMP association. All my edits are lost unless I either manually load the XMP again, or if I click in ACR on "Previous Conversion".
If I instead use Adobe Bridge to reset previous settings, Bridge errors out with "The Camera Raw settings could not be applied because there were no Camera Raw files selected or selected files were read-only.". I believe Bridge, unlike ACR, is trying to apply those settings to the DNG directly, which fails because the DNGs are read only, instead of just restoring the association with the XMP file.
All this starring and labelling works fine if I use fastRawViewer instead of Photo Mechanic. If I label in FRW, I can see the rating/color in Adobe Bridge (but NOT in Photo Mechanic), and the file opens up correctly, with edits applied, in ACR.
Also, things seem to work fine with normal, unlocked DNG files, though in that case the DNG file itself is modified (even though I set ACR to always generate XMP file). I am using locked DNG files, because my backup/version control system doesn't bode well with constantly changing DNG files. And I am using DNG files because I am using a 3rd party RAW convertor for my RAF (Fuji X system) files.
Photo Mechanic is configured with Adobe compatibility, as instructed here.
What's going on?