There is no Multi-Select Property for Comboboxes. This Property is only
available for Listboxes.
In order for a Combobox value, once selected, to show when you return to the
record, the Combobox has to be bound to a field in the underlying table.
The same goes for a Listbox , but it can only be bound to a field in the
underlying table if Multi-Select is set to No. A Listbox has no Value
Property if Multi-Selct is set to Simple or Extended.
To do something like this using Multi-Select, after having initially made
your selections, you'd have assign the selections to fields in your record,
by loop thru the multiple selections.