UIView animateWithDuration & UIView commitAnimations stops working strangely

Question

I have some animations on my app like this:

[UIView beginAnimations:nil context:nil];
[UIView setAnimationDuration:0.3];
navigasyonresmi.frame = CGRectMake((windowgenisligimiz-10)/4, 194, 10, 4);
[UIView setAnimationDelegate:self];
[UIView commitAnimations];

and like this

[UIView animateWithDuration:0.30 animations:^
 {
     [resimlerimalani setAlpha:0.0];
     [digerdetaylar setAlpha:1.0];
 }
 completion:^(BOOL finished)
 {
    resimlerimalani.hidden=TRUE;
 }];

They are working pretty fine, but when I start to do something on my application, like when I visit my pictures page, I'm loading all pictures in nsthread, everything works fine, but after something happen (I don't know what is it) all of these animations stops working, they are animating immediately, not in a time.

What can be reasons to stop whole UIView animateWithDuration & UIView commitAnimations in code ?