we faced very specific scenario in our Sitecore enviroment. In our Sitecore we have a item, lets call it "Promotion". Promotion was using "End date" field that was shared.
On our dev instance we "unshared" the field. Which naturally triggers the background process that changes the items to use field in unshared mode. Similar process is described here: http://sitecoreblog.alexshyba.com/2011/10/changing-field-sharing-settings-in.html So then we packaged and installed change of "unsharing field" on production "master" database. As I assume during installation the background process of "updating the items" has not been triggered. Which now behaves in the way, that "unshared" field on our production master database cannot be saved. Cahnges of value after clicking save are "vanishing". I am sure they are now being saved in some language agnostic mode.
Of course simple fix for that is to "share" it back and "unshare" it again. However when we tried to do this experiment on copy of our enviroment and we noticed all the values were lost. As the items from mentioned template are heavily used, we cannot really afford loosing those values.
Any ideas?