When Opera is open on a system, there are multiple processes running with multiple files open. If one of the open files requires correct closure from one of the processes when Opera shuts down, an "improper" PC shutdown may deprive it of that and result in file corruption or lost entries. The installed extension database may simply be the first or weakest link in the collapse chain. Trying to decipher the specific reason for peculiarities in the death throes of a program on an improperly shut down PC can be an exercise in frustration. There's a reason all software and computer makers will tell you never to "improperly" shut down a PC... which, of course, doesn't always reflect the reality of sudden surprises occurring beyond a user's control. But power failure is one reason I started using a UPS power system some time ago to avoid this sort of problem, at least from that cause.