DatePicker broken by ID with period

If the text input has an ID with a period (.) in it, such as

<input type="text" class="datePicker" id="user.startDate" />

the date picker will not set the value when a number is clicked. You get the error "elem is undefined" for

var id = elem[ expando ]

at jquery-1.2.6.js (line 662).

It appears the problem is that the period confuses the selector for returning to the element. Changing the ID to not have a period fixes the problem, but period-delimited input IDs are central to the Spring framework, so this can't always be worked around.