The display dates generated for e.g. browse indices are only generated correctly if the metadata date got no time granularity, otherwise the dates will be reduced to year only.
2010-04-22T09:17:01Z results in 2010
2010-04-22 results in 22-Apr-2010
This leads to wrong/mixed displays if
a) someone uses dc.date.issued in the display and got pre 1.6 data
b) someone uses another time stamp e.g. dc.date.accessioned with time granularity