Time-Lapse Jitter

[GingerGarden]

I'm using a Canon 60D with a 18-135mm lens.

I used an interval of 20sec and bulb ramping set on sunset with a max rampspeed of 0.05 EV/Shot.

The last couple of time-lapses that I have done produce a jitter during the first 250 or so frames, but after that it seems fine. The last one I did was tonight for a sunset and it was very apparent when the jittering stopped.

Here is the first time-lapse that I did that produced a jitter.  http://www.youtube.com/watch?v=TXWn_inn2ac&feature=share&list=UUJ7qLqVrdixquEoekNSILDA

Any ideas?