If file not changed outside Lightroom, just save metadata (from catalog to disk) to extinguish. - prolly a bug..
If Lr still unhappy, then read metadata (from disk to catalog) afterward.
Of course, make sure everything is backed up before doing such stuff.
Thanks Rob for reply.....will give suggestions a go and well it might be a bug as i have just done updates to LR5
Lr has been "metadata status challenged" since day 1 - if this is the first anomaly you've experienced, consider yourself lucky .