That is, I had to delete the trailing 978 (for "Bookland") and edit the last ("control") digit, from the 13-digits string usually produced by a barcode scanner.

A lot of times, that digit has nothing to do with the actual ISBN.

E.g., 9780486650159 should be edited to 0486650154. ^^^ ^ ^^^ ^

I think this is a bit unconvenient. Since I am a newbie to Koha, I wonder whether this is a feature or a bug: which way should one enter one's ISBNs, with or without the trailing 978?

Currently, that 978 is not part of the NISO standards. In a few years, it will be. See: http://www.niso.org/standards/resources/ISBN.html Cheers, Brooke @ Hinsdale MA