When using book drop mode in returns.pl, the checkin date is set to the last date the library was open. However, this gets confusing when multiple branches within the same system have different calendars. Book drop mode selects a date based on the calendar of the library whose circ rules governed the checkout (the library indicated by the CircControl and HomeOrHolding sysprefs). It does not consult the calendar of the library at which the checkin is taking place. This is not a particularly transparent behavior and is not explained in the manual. I'd like to see an explanation added to https://koha-community.org/manual/17.11/html/05_circulation.html#check-in-returning.