Did you delete the original files from within MC?
I guess if you ripped the files using something else, over writing the
original files, then MC wouldn't have known to reimport them?
Saying that if you have Auto Import switched on, with
"Update for External Changes" activated, then it should still pick
up the changes... if it doesn't then I'd imagine that's a bug.
So here are the steps:
1. re-rip files on my notebook
2. go to server, delete originals
3. copy from notebook to server
4. run import (files not imported, of course)
5. run import with "ignore deleted" turned off
6. new files show up with old bit rate
7. run "update with file data"
8. files now show right bit rate