Refresh button difficulties

Dear KNIMErs,

I am trying to build an application, where the user should be able to upload a spreadsheet file (xlsx) and once this is done, the should click a button to get an updated list of columns to choose from.

This is my current setup, however, the dropdown in the Value Selection Widget node does not change:

Whenever I choose a new file in the File Upload Widget in the interface, the Value Selection Widget node DOES NOT get updated. And I don’t really understand why.

Thanks in advance for your kind help.