These doubts lie in the mysterious lunar cycle. Ramadhan ends when the new moon is sighted; it is not enough to theoretically know which night the new moon appears--they have to see it with their own eyes to declare it official. Which means that if it's a cloudy night, Ramadhan ain't over yet.
Tanzania's Muslims often chose a day different from other parts of the world--apparently Tanzanian religious leaders tend to agree that they've seen the moon before others. I don't blame them. It's tough observing the fast here, because, as it's been explained to me, "in other countries people don't work that month. But here we're poor, and we can't stop working." Plus, less than half the country is Muslim--and Christians can't also shut down business for a month.
In any case, the end of this week will mark the end of Ramadhan. And we'll all get a long weekend, Christians and Muslims and pagans alike. Muslims might not be sure which day, but every Christian in town I've talked to is positive that the holiday will be Monday and Tuesday. Long weekend here we come!