After importing my files into iMatch all files came up with the pencil icon indicating that write back to files is required for XMP::dc\Subject. After making changes to the keywords the metadata needs to be written back to the files twice. I believe the first takes care of the metadata changes and the second write back is necessary due to XMP::dc\Subject.
Perhaps I'm doing something incorrectly or could be doing something differently to avoid write backs these two times.
This is normal when the XMP or legacy flat keywords are initially not in-synch with the hierarchical keywords (depends on your workflow and which applications you use). This may also depend on how you have configured IMatch to map between hierarchical and flat keywords. Nothing to worry about.