If an item is deleted while it still has an open(datearrived is null), uncancelled transit in branchtransfers,the receiving library will receive a 500 error when trying to view "Transfers to receive" (transferstoreceive.pl) If the item has a hold on it, Koha prevents the deletion. However, if the item is being manually transferred and has no hold on it, it does not. I'm not sure if this in any way relates to https://bugs.koha-community.org/bugzilla3/show_bug.cgi?id=32528
+1 agreed - items in transit should not be able to be deleted.