There appears to be a flaw in the calendar.js in the defaulttheme.jar file such that since February 2009 started on a
Sunday, ends on a Saturday, and has exactly 4 weeks in the month, the calendar fails for a Javascript error in function
ui_Calendar_redrawCalendar on a null reference to this.lastRow.  Below is the snippet that fails with the specific line
denoted by "--->":

if(linkNum < 35) {
        counter = 1;
        while(linkNum < 35) {
            link = document.getElementById(this.dateLinkId + linkNum);
            link.className = this.edgeClass; 
            link.innerHTML = counter;
            link.title = this.formatDate(first.getMonth() + 2, counter, 
                first.getFullYear());
            linkNum++;
            counter++;
        }
--->    this.lastRow.style.display = "none";
    } else if(linkNum == 35) {
        this.lastRow.style.display = "none";
    } else {
        counter = 1;
        while(linkNum < 42) {
            link = document.getElementById(this.dateLinkId + linkNum);
            link.className = this.edgeClass; 
            link.innerHTML = counter;
            link.title = this.formatDate(first.getMonth() + 2, counter, 
                first.getFullYear());
            linkNum++;
            counter++;
        }
        this.lastRow.style.display = "";
    }


This has been tested to fail on both a windows box and a linux box, both running tomcat 5.5.27 with JDK 1.6.0_11.