The constructors for the singletons for date-based FieldTypes (in FieldType.java) are constructed with the wrong Java datatype (I think). Fields that represent UtcTimeStamps for example, actually return a Date object from getValue().

The offending lines are:

public final static FieldType UtcTimeStamp = new FieldType("UTCTIMESTAMP", Calendar.class);
public final static FieldType UtcDateOnly = new FieldType("UTCDATEONLY", Calendar.class);
public final static FieldType UtcDate = new FieldType("UTCDATEONLY", Calendar.class);
public final static FieldType UtcTimeOnly = new FieldType("UTCTIMEONLY", Calendar.class);

I think the "Calendar.class" should be replaced by "Date.class" at the end of each constructor call.