Comment 12 for bug 507836

It looks like the following is triggering this problem (a clasical race condition):

- a update() operation from the backend (reload, enable channel) triggers a apt-xapian-index update with --update
- when the update is finished, a cache-ready signal is emited, that causes the various views to be refreshed
- during this refresh the gtk event loop keeps running to keep the UI alive
- when apt-xapian-index finishes, it reopens the DB
- if the a-x-i update finishes quicker than the refresh triggered by the cache update finishes (its runs with --update so that can happen) then it can be in the middle of a "for m in self.xapiandb.postlist() operation. at this point the returned iterators are no longer valid because the DB got reopenend and xapian detects that (the iterators are for the previous generation of the DB)