Dates Not Matching

I have a TreeMap of <DDate, Integer>.

DDate just contains month and year (month is 0 indexed, like in Java, JAN = 0);

My compare is not returning the right thing:

@Override
public int compareTo(DDDate o) {

    Calendar cal1 = Calendar.getInstance();
    cal1.setTimeZone(TimeZone.getTimeZone("UTC"));
    cal1.set(year, month, 1); // year is 2012, month is 1

    Calendar cal2 = Calendar.getInstance();
    cal2.setTimeZone(TimeZone.getTimeZone("UTC"));
    cal2.set(o.getYear(), o.getMonth(), 1); // year is 2012, month is 1


    Log.log("COMPARING: " + format.format(cal1.getTime())); // COMPARING: 20120101
    Log.log("COMPARING: " + format.format(cal2.getTime())); // COMPARING: 20120101

    Log.log((cal1.getTime().getTime())); // 1325413927678
    Log.log((cal2.getTime().getTime())); // 1325413927679

    Log.log("WILL RETURN: " + cal1.getTime().compareTo(cal2.getTime())); // WILL RETURN: -1

    return cal1.getTime().compareTo(cal2.getTime());

}

Why is there descrepancy in the two Calendar objects for the same Date? (1325413927678 vs 1325413927679)

Thank you!

FYI: this method works for a while, and then at a certain point, stops working.

P.S. - I understand this is overkill, I can have a simpler compareTo, but please humor me.

EDIT- FIX

Use JodaTime's LocalDate.

Or do this:

Calendar cal1 = Calendar.getInstance();
cal1.setTimeZone(TimeZone.getTimeZone("UTC"));
cal1.clear();
cal1.set(year, month, 1); // year is 2012, month is 1