Specifying yearRange on datepicker causes it to stop showing month/year dropdown lists

Specifying yearRange on datepicker causes it to stop showing month/year dropdown lists

By default datepicker shows lists for month and year (see Capture1.png)
I need to limit the year range, so I specify:
$( "#PurchaseDate" ).datepicker({ yearRange: "-0:+20" });
 
But when I do, the datepicker no longer shows the drop-down lists, but instead only has left/right scroll buttons (see Capture2.png)
 
???
 
DadCat