gnome flashback session logging out mysteriously

[Adam Funk]

My kid's computer has a clean installation of 14.04 on it.  He uses
gnome-session-flashback, & for the past week or so has had occasional
problems with it logging itself out while he's using it.  There
doesn't seem to be any pattern --- it might happen while watching
youtube or playing Minecraft, but he says that when he is doing
Scratch programming, it only happens right after he saves
(fortunately, in a way).  Has anyone ever heard of this?  

(I tried googling for it, but queries that include 'logging out' or
'logout' bring up a lot of false positives; I could get 'accidental'
or 'unwanted' or anything like that to work.)

Thanks,
Adam