Thanks for your reply. We have tried what you have suggested, that is making the following call.
It seems that this will force the combo box to reload fully. However, the items are not available at the appropriate point in the page life cycle for us. So, it doesn't really solve our problem because what we need is to, as per my original post, to be able to
"force the combo box to load by calling ComboBox.DataBind() in the code behind."
Is there any way that this can be achieved? Please let me know if you need any additional information.