Well, the time until it's next due is also influence by the items "due-ness" percentage when you reviewed it.

For example if you review word A when you should (i.e. at around 100% due) it's rescheduled for a certain amount of time (based on shortly before you're likely to forget it again).
Now if word B is already 400% due (e.g. you were supposed to review it after 1 week but for some reason you only got around to it after 4) and you still got it right, the word gets pushed back much further -- the reasoning being that you know the word better than the SRS anticipated.

Malaili, do you use the "So-So" or "Easy" gradings? These also change the timings a lot, but even "so-so" is considered "correct".