NSTimer thread issue

Question

I have singleton that implements NSTimer object.

I run my timer using code below

self.myTimer = [NSTimer scheduledTimerWithTimeInterval: 1.0
                                                        target: self
                                                        selector: @selector(onTick:)
                                                        userInfo: nil repeats:YES];

I have NSUInteger instance variable that increase at each time when - onTick: method is called (so, once a second).

I have UILabel that represents date of my NSUInteger instance variable and it works good. I have UIScrollView in my view as well. When I am scrolling it my UILabel does not update text. Even NSLog that shows info about timer tick in - onTick: method does not work. If I don't scroll timer begin works.