Backupset daily.1 always being overwritten

Jason Collison (collison.1 at osu.edu) reported me the following issue:

I have been having difficulty getting backupninja to properly use the
rsync method. Can you problem shoot this? Basically, the backup process
itself seems to work fine, but the rotation process seems to not work.
For example, if I'm bacting up /etc, things start of okay, I will get a
backup in /backup/etc, but after ~3 days, I start getting warkings that
/backup/etc/daily.1 is going to be overwritten, and I never get more
than 3 daily backups even though I have specified 7. I also never get
any weekly backups or monthly backups even though I have those specified
to.

Here is what my configuration looks like:

[general]

mountpoint = /mnt/backup
backupdir = spirit
format = long
keepdaily = 7
keepweekly = 2
keepmonthly = 6

[source]
from = remote
host = spirit
user = root
testconnect = no
protocol = ssh
include = boot
include = etc
include = home
include = root
include = var

I'm running gentoo with backupninja version 0.9.7 (the only version
currently in the portage tree). I have upgraded the rsync helper file to
version 0.9.8.1 hoping that would resolve the issue.

(from redmine: created on 2011-06-04, closed on 2012-01-04)