Full signups getting reopened via cron

My signups that have been closed because all available slots are full are being reopened by cron. This only happens when the signup schedule close event date is still in the future. After I signed up, the signup module closed the module as full, only to be reopened yet again by cron.

After I disabled the signup scheduler module, I ran cron manually and the problem was solved (the full signups remained closed).

I am running the following:
Drupal 5.6
MySQL database 5.0.45
PHP 5.2.5
Apache webserver
Event 5.x-1.0
Signup 5.x-2.4
Signup Scheduler 5.x-1.0

I'm also running Signup Restrict by Role 5.x-1.x-dev, but I don't think that would be contributing to this issue.

Also, when I went to admin/content/signup the affected signups' statuses were listed as "Closed (limit reached)". However, when I went to the signup page, I was able to sign up (perhaps an issue with the signup admin page code not related to this issue, but wanted to make a note of it just in case it was useful).