GAE expanded log view
App Engine stores logging information in a set of circular buffers. When it runs out of space, it overwrites older log entries with the new data. What you're seeing is requests for which the detailed logs have been overwritten by newer requests.
This might not be bug, but feature. I'm having problem views expanded logs when searching logs in dashboard on app engine. 
Search results show first couple of logs in full detail, but rest of log entries are obscured. Every new entry in log is shown in full details, but older ones get obscured over the time. 
Same behavior is reflected if I try to download logs from app engine, only more log entries are not obscured. 
Point is that I can't get full log of my app and would like to be able to run some tasks over data.