Did you wire them yourself?
We seem to only have one type of battern over here, well two but I find those difficult to work with.
I have had some similar issues and although I cant say for sure these are the only reasons I can offer:
1: May have pushed wire through to much so that it shorts through the globe.
2. I was having problems with a cage that did not have chord access built in and although I grooved wood to allow chord to go under cage it still heated the cord enough to cause issues.
I hate these things, gets me very parinoid. Yet other enclosures have never given me any grief.
There are three types of themo, on/off (on till temp is ok then light is turned off until temps drop)
Dimming - like the dimmer switch for house lights, so lamp never really is turned compleatly off but heat increased or decreaed by altering power supply to globe.
Pulsating - These are often for ceramics and heat chords that heat up and contiue to do so after power is removed. On this priciple the themo provides a bit of power, cuts it and measures temps and then provides some more as required, thus it pulses.
Hope I have got all this right.