Comments automatically closing on older posts?

For some reason, I am noticing that all my posts older than a month or so are automatically closing comments. I looked in the settings, and I have nothing checked to close old comments. I have no plugins that are set to do that-I have the following plugins in use:

Akismet 2.1.8
Comment Referrers 0.1
Post Revisions 0.1
Snap Preview AnywhereTM Plugin 1.0
StatPress 1.2.9.2
Subscribe To Comments 2.1.2
WordPress.com Stats 1.3.2
WordPress Database Backup 1.7
WP-Amazon 2.0 Beta 1.1
WP-phpMyAdmin 2.10.3

I see no settings in Akismet to close old comments automatically, nor anything in comment referrers or subscribe to comments, and it wouldn’t really make much sense for them to have those functions I don’t think.

I can’t figure out where to start looking to check to make sure no code or plugin is causing this to happen. I found a code to use in phpMyAdmin to globally open all comments in all posts, but for some reason I’m getting an error that won’t even allow me to use phpMyAdmin right now.

Any ideas what could be causing this? Any idea where to start investigating? I’m not all that good with code or changing php/sql settings, knowing what blocks of code means, etc. It’s been a while since I’ve made any changes at that level, so I forget much of it…

I was able to test and go into several old posts that automatically closed comments and reopen them by choosing “allow comments” and “allow pings”…if you go to the posts where they closed by themselves, the box next to “allow comments” is unchecked.