[Koha] ISBN 13 to 10

[Paul]

Would some kind soul with "corporate memory" please give me background on 
*why* the staff-admin page (basic search, search.pl) converts a 13 digit 
ISBN to the "old style" 10 digit format?

As soon as you click on the title the details.pl page gives the 13 digits 
as entered in the biblio record (and for completeness the OPAC appears to 
only use the 13 digit format.)

The reason for the query is that our cataloguers have pointed out that an 
"advanced search" for ISBN on the truncated, recalculated value, gives a 
"No results match your search for 'nb: 1551250934'" while the full 
9781551250939 (i.e. with 978 at the beginning and correct check sum) for 
the same book finds it instantly.

At some point in the past, someone must have considered this a "desirable 
feature" -- I'm intrigued as to the reasons.

Thanks - Paul