Our application sometimes couldn’t recover from Tombstoning. When the problem happens, it becomes impossible to restart the app with the debugger because the debugger complains that there is a file in use. Uninstalling and re-installing the client does not help to fix the problem. The phone needs to be restarted.
After some investigation, we found that the debug log file is not closed correctly in the de-activate phase. Note that this problem only occurs on the Lumia 900 and not the Lumia 800 or 610.
The moral of this story: Be careful to close your debug log files when tombstoned.