Commit selected value immediately (CommitOnSelChange) not working in Viewer

I have a Form PDF and a Combo Box, and I need to apply the changed value inmmediately for the Save Button to appear in the Viewer.

The Save button only appears if I click elsewhere on the page, outside of the combo box.

I have selected the option: "Commit selected value immediately" (CommitOnSelChange) in Combo Box Properties, but it doesn't seem to work in the Viewer.