Scanning progress dialog stays visible even when the scan is over

From e-mail:

I launched a new scan, hided DupeGuru, showed once sometimes later then re-hided it. When I came back several hours later I found the progress sheet still opened , frozen in Matching at 12000/70000 (perhaps the exact count when I hided the app the second time.) but the scan was actually finished and the appl responded correctly (except the buttons in the toolbar but I could use the menu equivalent). I've been able to trash de duplicates (then, as the process also used a sheet , it closed normally.) and quit normally.