Been watching Doctor Who (from the 2005 season) for a while now and it’s disturbing how inconsistent they can be at times with the rules of time travel in a series centered around time travel.
If a human goes back in time and saves someone who died, that creates a time paradox, with strange creatures appearing, the TARDIS becoming an ordinary wooden box and so on (cf. episode 1×08 Father’s Day). But if a time lord goes back in time, and saves people whose death had a significant impact on history, then nothing happens, except for a few words changing in future newspaper articles (cf. episode 4×16 Waters of Mars). Decide if changing the past creates a time paradox or just changes the future.
Also, why is the Doctor surprised at every single alien appearing in town, claiming “this shouldn’t be happening” or something along those lines, when he’s seen the future (damn, he was remembering the articles about the Mars expedition in the aforementioned episode), he strangely doesn’t know anything about events that concern him.