[Koha] Which ISBN is searched for by Z39.50 ?

Hi again, when I used to have a Z39.50 daemon working under RedHat 9.0 with a 1.x version of Koha, I noticed that I could _NOT_ search ISBNs in the format 978...X. 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. 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? Thanks again. Giuseppe.