Tagging is controlled by:
a) the setting Options > General > Importing & Tagging > Update tags when file info changes
Also available under Edit > Update Tags When File Info Changes
b) individual library fields: Options > Library & Folders > Manage Library Fields > * > Store in file tags (when possible)
When you change properties in MC, they will be automatically written out to files soon after they are changed, provided both (a) and (b) are set.
Tags in files will be created as needed if they are in MC.
MC won't just lose your file properties. The info would be in the DB. You probably did something to delete the info.
You can verify physical file tags by selecting a file, and going to the Action Window > Tag, and clicking on the file type shown just under the "Tag" heading of the Tag action Window (hover your mouse, and you'll see a tooltip "Click for detailed format information").
http://wiki.jriver.com/index.php/File_Properties_%28tags%29You can manually request MC to write out tags with Library Tools > Update Tags (from library)
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