I've run into a problem when using a Combo Box for a Multi-Select Parameter.  The issue is that if the user selected values then clicks the preview button, while the dropdown list is still displayed, the parameter is not set before the report is generated. 

I would prefer to use the combo box to set the parameters, but this will be an issue for the users. If I click elsewhere on the report or just re-run the report the parameters are set properly. This does not occur with the Listbox functionality.