Don't trust your eyes when looking at weak pointers
We have some really old piece of code. It’s basically a proxy for an NSTimer retained by the timer instead of our precious View Controller that shows the PDF file. The code was written in the manual reference counting times, then semi-automatically translated to ARC and left for good. Turned out that all these years, since the translation to ARC, it had a bug that led to a leak that went under the radar of leak detection tools.