How can this happen?

[Paul5388]

If/when I decide to tumble a batch of brass, I normally make a practice of blowing compressed air through each primer pocket. With 100 psi of pressure through a rubber tipped blow gun, it usually ensures a media free case.

 

[thedane]

FWIW, I used to decap before I cleaned my cases. Then you have to worry about the flash hole and media. Years ago I started cleaning my cases before decapping. Now it's much easier and no worries about the flash hole being clogged.