Well, Flickr have so far sent two emails to say it's a "known issue" and they are dealing with it as fast as they can.... which it seems is not very fast!
So I have hand-made the galleries by just downloading the pictures from Flickr and naming each picture with its description - Juicebox does the rest!
I think Juicebox is such a fantastic application and it works really well.
Thanks for all your advice, which is also reliable and helpful.