This is a weird thing. I have seen times that the auto focus do not work when using the ZBarReaderViewController. What is "low memory"? Well, this is a litle more complex, because the iOS do not send a memory warning.
The last time i see this, I first open a ZBarReaderViewController. Then I receive a memory warning, and this automatic close the object. Than I open the camera again. This recreate all new objects (this completed released the olds one). Than the auto focus do not work. I switch between ZBarReaderViewController to ZBarReaderController (my app do this) and the focus work again (I switch again for ZBarReaderViewController and now work)
So, in resume: There are times that autofocus do not work. And this is because the memory is low, but the iOS do not send a memory warning. I have seen other times that autofocus do not work, and I think is all because the memory.
Is this a ZBar bug? Or is a iOS bug? If is a iOS, there are anything we can do? There are a way to check if autofocus is working or not?
I see this in a lot of iPhone, using iOS 4 and iOS 5. The ZBar is the last one, 1.2