To re-create 1/ Go to Circulation->Fast Cataloging 2/ Add a biblio record 3/ On Add Items screen, enter a space in 'Koha out on loan' (and enter item type of course). Save the item. 4/ items.onloan will be set to 0000-00-00. ... I'm not certain whether or not this is specific to the fast add framework. Note that this causes upstream issues with search -- any item that has items.onloan set to 0000-00-00 will cause an internal server error on the search results page, with the following error in plack.error.log: Can't locate object method "ymd" via package "dateonly" (perhaps you forgot to load "dateonly"?) at /usr/share/koha/li b/Koha/DateUtils.pm line 223.
"Koha out on loan" does not longer exist, I have tried to put space in a date field and I do get a crash. Assuming this is fixed.