Starting and Running Problem...

This reminds me of something that happened to me a few years back. I had just finished installing a pretty healthy brand x street/strip motor that I had freshened up for the guy, went from a solid to a pretty healthy mech. roller, made some other changes. I had set the timing, re-torqued the heads, restricted the idle feed, as it wasnt responsive to the mixture screws, re-lashed the valves hot. After I did all this, He had cleaned the plug wires with soap & water, I put em back on, going through the firing order as I went, & we were out on the first test drive. It also had an MSD 6A on it.
So at first, it was running like gangbusters(the car ran 11.04 next time out, eventually ran 10.90s with the same combo), but then it started to miss on one cylinder, so I told him to pull over. By the time we pulled over, another cylinder had started missing. So we get out, lift the hood off, and there are two plug wires off, laying on the headers. I am kind of baffled, because I was damn sure I had pushed them all on tight. So I reached down to check another plug wire, and when I touched it, there was a small pop and it popped off the plug into my hand. For a minute or two I was THOROUGHLY baffled, standing on the side of the road, scratching my head. Then I started laughing...
Anyone wanna hazard a guess as to what was going on? Ramcharger will probably nail this, but pm me, and lets see if some of the others can figure it out before you respond.