I just set one up and don't seem to be having an issue. Ran an import, created a process for the import. Then published it to the dashboard and was able to have it prompt me. I thought it might be if you have the same file in the same place and you run the process it might not prompt you, but I ran the process multiple times and it prompted me every time.
Are you still having the issue?
I might be missing something, but I don't see this to be working. I tried changing the location of source file, and it never prompted for file (when I run it neither from process pulished on dashboard nor list of actions/processes). Appreciate if you can share details of how this actions has to be setup.