I have had the same thing happen with a merge, as I was doing the merge and cleaning up the biography, I noticed some sources missing, went to look for them, spent less than 5 minutes, but after all the edits, I hit save, it went to another page and I got a session timed out message. The problem is that during a merge you cannot do an incremental save. So, I guess in the future I will just back out of the merge and then do the research. One of those "would you like to continue" messages would help.