Hi Bernhard,
The importer will always try to re-use previously imported venue and organizers, however this hinges on them truly being the same entity on Facebook (and not merely sharing some/most of the same details).
Can you point me to a couple of the different Facebook events you have imported from so I can try to evaluate if each venue is actually the same entity?
Upon making a quick test (where I know the venues for a series of different events are genuinely one and the same) I don’t see the problem occuring – but I can certainly look into it and checkout the actual events used in your scenario.
(I also note your license for Facebook Events seems to have expired, so though we’re always interested in bug reports there may be a limit to how much help we can extend here.)
Thanks!