After some recommended log statements, I've found where's the problem:
In iOS6 the height of the UITableView's frame turns to 0. During "viewDidLoad" the height is correct(94p), but after that the height is always 0.
But I really don't know why this is happening. In iOS7 the UITableView's height never changes.
So I can "fix" it by re-setting the UITableView's frame height in "viewDidLayoutSubviews", for example. But if anyone has a clean way of fixing this, or knows the origin of this behaviour, it will be appreciated.