Created a new edit bucket. Selected everything (by leaving all fields blank) and was shown the "add all 609" auctions to this bucket" button. Pressed that. Went through to put in the changes.
Selected description replace X with Y (not literally!) and clicked to perform.
Was taken back to a screen saying I'd got an incomplete bucket. Clicked to "carry on". Have now been round that loop three times adding everything to the bucket, and it keeps telling me the bucket is empty. Tried forcing it through to make changes, but the bucket is empty.
It's not an urgent change, so I've left the "empty" bucket there for you to look at in case you can see anything odd going on.