Adding a repeatable holiday creates holidays retroactively for Koha’s calendar
module.  fines.pl balks when it sees an overdue fine calculation where amount
!= amountoutstanding (it assumes a payment was made, so tries to adjust the
amountoutstanding appropriately).  This fails if the calendar module reports a
smaller number of fine-inducing days on one run of fines.pl than it did on the
previous.

Symptoms:
Overdue charges appear on patron accounts with Amount Outstanding > Amount.

This problem only occurs after a library has changed its calendar settings.  Adding Sunday as a repeatable holiday, for example,  makes Koha erroneously added the retroactive fine amount ($1 per day for movies, .05 per day for other items) to the maximum total, resulting in nutty fines like $3.25 (for books and other items) and $7.00 (for movies).

When you run across these kinds of fines, just charge the patron the $3 maximum and “write off” the remainder by paying the whole thing off regardless of the actual amount. The bug will be fixed eventually.

Mickey