I was working with a customer who had a tag used for associating a specific document with a geography/region as shown in the image below. Managed metadata columns are a feature in SharePoint 2010 permitting you to add specialized/pre-defined term sets to a particular content type. In my customer’s case, they had a document library with a Geography column.
Elevated users could add documents, specifying a value for the Geography field without issue. ‘Normal’ (Non-site admin) users could also specify a value and save a document to the library without error; however, the field would not be populated with a value upon saving the document. (The managed metadata column would simply be blank.)
The hidden taxonomy list (accessible via the following url: http://<sitecollectionURL>/lists/taxonomyhiddenlist) had been modified by some automated tools ran in the customer’s environment and had removed authenticated users from this list; hence the reason why site-admins were able to properly add records but domain user’s could not. Adding nt authority\authenticated users back into this hidden list resolved the problem. Hopefully this saves you some pain in tracking down this problem if you’re impacted by it!