Help with lights!

I didn't know what section to put this question under so i did it here. My wife has a 99 chevy blazer and i put some clear taillights on it. they were fine on there didnt have any problems or anything. one day i noticed that the damn things were pretty much melted to the ride. i had to pry the damn lightbulbs out of it. when i seen the lightbulbs the bottom of them were melted to the socket. i had to pull them out with some pliers. the sockets were all black and everything but i put some new bubls in and they worked just fine. i put the stock taillights back on and havent had a problem since. i was just wondering if somebody might know why that happened because i had them on there for the longest time before it happend. now i know that the taillights pretty much had to have melted overnight cause i would have noticed it before. i would appreciate any feedback. thanks.