If the calendar has concurrent holidays, when holds_reminder.pl cronjob is being ran daily with the --triggered switch and the day the notice should be sent lands on a holiday which is repeated the following days, the cronjob sends holds reminders until the holiday period ends.

To reproduce:

Reserve an item, receive it at a branch where the reserve was made to.
Move the waitingdate and reservedate of the reserve to x days before the reserve was made in the database. 
Add holidays (single non-repeated days) to the calendar so that the first holiday lands on a date when the hold reminder should be sent.
Set up the cronjob to run so that the --days trigger matches the first added holiday using also the --triggered switch:

holds_reminder.pl -v --days x --triggered --holidays -c

for example. Check that the x:th day from the reserve's waitingdate is a holiday, and the date has following days set as holidays as well.

Notice that on the following day/days of the first sent reminder, the message is sent again. Same happens the following holidays.

It seems the notice is sent also if there is a repeated holiday following the first single day holiday the message was sent (like if saturdays and sundays were repeated holidays).

I guess this could be reproduced easier by moving your system date forward and running the cronscript again. I couldn't reproduce the same bug when moving back the waitingdate of the reserve to simulate a day had passed since the first message for some reason. Notice that modifying the holidays use a cache, so just making changes to the database is not enough for the cronscript to notice the changes made.