Caching of SELECT options

I have a web form in which the options of a dialog list are populated at run-time using JavaScript, based on information taken from other fields. The problem is that when I display a validation error message and go back to continue editing the form, the dialog list has no options (or values). I tried @SetHTTPHeader(“Expires”; “0”), which seems to work for other field types, but not for dialog lists.

Any ideas? Thanks.