I've never done it - YET - but I have come very close to it - but sooner or later, it happens! By the same token though, I have forgotten to cap my rifle!
I can remember being at an informal shoot with about 7 or 8 guys one Sunday - we were taking our time and just having an elimination shoot - I think we were shooting at cans or something. We were all standing there watching one of the fellows reload his flintlock rifle as he was up next and I swear that none of us even caught on that he hadn't put powder down the bore - and we were all watching him load! So I guess you could say that all of us were "boneheads" that day!
Glad you were able to get it taken care of and hope it didn't spoil the rest of your shooting time - just remember our forefathers had the same problems we do!