A Flaming Empty

[kt]

This morn bright and early i unleashed my wrath on a bunch of about 8 mallards, smoked two pretty well but i really flinched after the last shell ejected like a tumbling fireball hit the mud burning and the empty breech stood locked open with fire coming out, not a spark, a steady flame that i readily blew out then stepped out the empty. What the hell?
any body else have this happen, any ideas why? not looking forward to a repeat, to close to the face for flaming projectiles. thought maybe rem-oil caught fire but the flame was real steady out of the empty and rem-oil has never done that in 10 years. rest of the day went fine a whole limit died.
kt