Funny, I just returned home from unloading my flintlock, I loaded it the first week in December and haven't shot it since, I have left it locked up in my storage shed...I primed it, set the trigger and she went off with no problem...I do not believe your patch contaminated the powder...I lube with SnoSeal, no over the powder wad, no problems...
Now, I am going to open up a can of worms...This is where a flintlock has an advantage over a percussion gun, no nicks and crannies for oil, grease to gum up the works and cause a barrier between your flash channel and powder...The powder in the barrel is just a few thousandths of an inch from the powder in the pan...If you have dry powder and a sharp flint, your gun will go off...
My bet is the problem is in how you are cleaning your rifle and leaving something in the barrel or drum causing the problem...
Ok, let's see if we can get 8 pages of discussion on this one!!!
btw....Of course I use a .54 as my deer caliber and of course I mold my own balls and of course I have enough flints, powder, lube and patching to last me the rest of our life, doesn't everyone???