What cause phase shift of color signal in NTSC?

As I understand there is colorburst signal before each line in NTSC. So chroma QAM signal is resynced many times per field. If so how it's possible that color shift occurs. How it is possible that color shift is equal in many thousands of consecutive whole fields (so manual tint compensation is possible)?

One, operator error or equipment miscalibration. Color burst and sync are regenerated at many points in the signal chain and it's possible to get the phase wrong - especially when mixing signals (delay errors) or playing back a consumer video tape. Two, . Burst is at zero IRE, visible chroma signal goes from -20 to +120 IRE, IIRC. Phase distortion can creep in. Three, burst phase detection itself can be in error. It's a complex bit of circuitry. Four...?

Thank you very much raffriff42. Now I understand. Most articles described NTSC color distortion as coming magically from "transmission" during bad weather.