When editing sprint date in italian language. I just set the start date and sprint lasting but end date textbox is disabled (with automatic content) and shows an error, so I can't neither edit nor confirm dates.

It seems to happen only when selecting a day in months where italian and english name are different like december (dicembre) or october (ottobre). 
The error disappears when selecting months like april (aprile) or november (novembre) so, to fix this bug developers should set field format and validator format the same in one of local or invariant language.

Thank you!