On 5560 the Revert command doesn't work with DNG even though they are technically "TIFF-based RAW". But DNG is not a proprietary RAW like CR2, NEF, ARW, ORF etc. We are changing PM to allow Revert on DNG, but rather than backup the XMP to a sidecar (which is not recommended for DNG), we re-embed the XMP.
However, if you go back to 5560 and simply do something like tag/untag then hopefully this will fix the DNG. It will "internally" do a revert then re-apply XMP as needed.
If this does not work we definitely need a sample that is broken (and if you have the "before" that might help).
We apologize for this bug but for the most part it is fixable in 5560.
--dennis