I am using Cocoon 2.1.5 and it has been in Production since 2004. I am also using the matt-kruse java-script library including the calendar widget.
A user has reported a “date bug” where if specifies a date that is between today and Feb 29, 2008, then it is saved correctly to the database, but when retrieved, it is one day less.
It does not matter if the date is entered directly into the field, or chosen using the Matt-Kruse calendar widget and so I surmise it has nothing to do with the Matt-Kruse date library, but I am not sure
Dates before Feb 29 work correctly and dates after today also work correctly.