datepicker with 'numberOfMonths' and 'yearRange' defined only shows 2011 in january 2011

When attaching a datapicker to an input element using the dateRange and numberOfMonths functionality, the only year shown is 2011. We are using:

jQuery: 1.4.4

jQuery-ui: 1.8.7 (custom, everything included)

FireFox: 3.6.13

OS: Mac OS X Snow Leopard 10.6.6

Actualy behaviour:

Only 2011 is shown in the year select

Expected behaviour:

Years 1931 - 2031 should be shown in the year select

Example code to reproduce:

// add datepickers to date fields
function attachDatePickers() {
	$("input[type=text][rel$='date']").each(function() {
		$(this).datepicker({
			changeMonth : true,
			changeYear  : true,
			numberOfMonths: 3,
			showButtonPanel: true,
			dateFormat  : 'dd/mm/yy',
			yearRange   : 'c-80:c+20',
			altField	: '#' + $(this).attr('name') + 'Example',
			altFormat   : 'DD, d MM, yy'
		});
	});
}

And the input element(s):

<input name="startdate" value="" rel="date" maxlength="10" size="10" id="startdate" type="text">

<input name="startdateExample" class="isExample" disabled="disabled" size="30" id="startdateExample" value="" type="text">

Workaround

The issue can be pinpointed to the 'numberOfMonths' property. When 'numberOfMonths: 3' is commented out, the year range is shown as expected (years 1931 - 2031 are shown in the year select element):

// add datepickers to date fields
function attachDatePickers() {
	$("input[type=text][rel$='date']").each(function() {
		$(this).datepicker({
			changeMonth : true,
			changeYear  : true,
			/*numberOfMonths: 3,*/
			showButtonPanel: true,
			dateFormat  : 'dd/mm/yy',
			yearRange   : 'c-80:c+20',
			altField	: '#' + $(this).attr('name') + 'Example',
			altFormat   : 'DD, d MM, yy'
		});
	});
}