应用程序在执行后台提取完成后处理程序崩溃

I have updated our app for iOS 7 and added the background fetch functionality. However, i'm noticing some crashes because of this feature. After background fetch call is completed, the completion handler block is executed with either new/no data. This results in a call to 'layoutSubviews' of my custom navigation NavigationBar and sometimes app is crashing with the following stack trace. I could not reproduce this issue myself but constantly receiving these crash logs from our users. Any help would be appreciated.I have updated our app for iOS 7 and added the