Pixel Crushers Forum

I'm still not sure why these files are getting marked in the first place, but I found out that Unity also has a related setting "Check the content to determine files as changed, not just timestamp" under Project Settings > Version Control > Unity Version Control Settings
So far enabling this setting in addition to the setting in Plastic SCM has fixed the issue.

Thanks for sharing that tip. There are some operations in which the Dialogue Editor may touch the timestamp but not actually change the file. Your solution is the way to go.