Cross Browser Issue with DatePicker

I've discovered an interesting issue with the DatePicker.
First some background:
I have a page with a Search Form, the results appear below the using
jqGrid. The Search Form has 2 fields where user can enter Date Ranges.
The user can select a row in the Grid and click Edit which opens a
modal form (jqModal). This form has 2 fields where the user can enter
a date. There is also a jqGrid on this form.
The user can select a row in the Grid and click Edit which opens a
modal (nested jqModal). This form has 1 field where the user can enter
a date.
The DatePicker has Month and Year drop downs that do not always work.
IE 7: DatePicker drop downs work on Search Form and 1st Modal Edit
Form, but do not work on 2nd Modal Edit Form.
Safari 3: DatePicker drop downs work on Search Form, but do not work
on 1st and 2nd Modal Edit Forms.
FireFox 3.0.1: DatePicker drop downs work across all forms.
I have been unable to discover the cause of this. I'm posting in hopes
that someone else has ran across this problem and found a solution or
workaround.