Ceramic heat lamp melted??

[Drizzzt5]

So I've had a 150w ceramic heat lamp to keep my enclosure temps up at night and when it's colder than normal. I've had it for about a year and plugged it into the zilla temperature regulator that turns it off when the probe reached a certain temp. Today I noticed that the lamp was cold even though the temp regulator said it should be on. I unplugged it and tried plugging it directly into the outlet and a spark flew out. I unscrewed the bulb and the part that screws into the lamp is black and melted. Any ideas as to what caused this?

Also the bulb was plugged into a dome fixture I got from Petco and it's max watt is 150.

 

[CooperDragon]

Sounds like it malfunctioned for some reason. I'm not sure what caused the melting. Did the bulb come in contact with any plastic? They get very hot and can easily melt plastic if it comes in contact.