Scanning downloaded files

NIS2012
Vista Home Premium 32 bit
Vista SP2

Ok I went ahead and downloaded the flash player uninstaller from adobe. Saved it to my desktop. In the process of saving NIS scanned it and said it was good. Ok no problem there.
So I ran it. Then rebooted my pc. I deleted the uninstaller.exe
For some reason I felt like I wanted to run the flash player uninstaller again. So I went to adobe site and downloaded it again. But this time NIS did not scan it as I downloaded it to my desktop.
Shouldn’t it have Been automatically scanned on download again?