Dropdown (Multi Select) Sheet Column In A Form


I have a Smartsheet column configured as a Dropdown (Multi Select) column type and do not have the checkbox ticked for "restrict to dropdown values only". While entering data in the column within the sheet itself I am able to enter values in addition to those provided in the field's value list. However, when I attempt to do the same via a web form I can only select from the field's value list and cannot enter additional values. I'm wondering if I don't have something configured correctly or if this is a form limitation?