I downloaded your scene, loaded it up, hit render sequence and it started rendering from Frame 140 and carried on from there, Starting frame = 140, End frame = 1450, Sequence step = 1. So the file is working as expected from here.
The only time I've seen anything similar is when using a render farm manager and the settings were not set up correctly, but your not using a render farm manager are you?
Odd ...
Richard