3.1L spark plugs loonening?!

So about three months ago, I had to have the upper and lower intake manifold gaskets replaced on the 1996 3.1L Lumina. Since he was in there, and had it apart, and since I had a cracked exhaust manifold, I had him replace that as well.
Question is this: Has anyone experienced the spark plugs loosening on their 3.1L engine?
I ask because about a month ago, I started having hesitation problems, and changed the wires, the air filter, the MAF. The MAF came up twice on the computer, once by itsel and once with a misfire. Since I thought the MAF may have caused the misfire, I changed it and it seemed to fix the problem.
Tonight, however, I decided to replace the plugs, too, as I was doing some other tune-up stuff, and when it came to two of the plugs on the rear, they were so loose I didn't even need the wrench to break them out! Just finger tight, and barely that! I don't know if the mechanic had to remove them and then forgot to tighten these, or what, but that certainly could have been some problems!
So, has anyone else had the plugs loosen?

If tightened properly the plugs will not loosen, even if they were left loose they may not loosen further because the wires may keep them from turning :bananasmi

Mark