metal450 said:

When editing a post, I noticed that toggling some of the checkboxes under "eligible groups" for "readers" also toggles the checkboxes for some of my categories.

It's not just the groups checkboxes, and not just in the Readers metabox. The same thing happens with the user checkboxes inside the Contributors metabox. The correlation is a "value" attribute that matches that of a category checkbox. That's not supposed to be treated as a unique ID in itself, since in this case it only distinguishes among the members of a checkbox array - post_category[] or r1g[].

I don't like to speculatively pass the buck before I'm sure. But this occurs even if I disable all other plugins and all Role Scoper Javascript. It sure looks like WordPress is inserting some errant JQuery that hooks onto the click event of any checkbox array, rather than just the post_category checkbox array. My guess is it just went unnoticed because there aren't any other checkbox arrays present on the default Edit Post form or inserted there by many plugins.

I plan to look into this more on Monday, but if you're in a hurry to get it resolved you might get farther with someone who really knows the WP JQuery code.

metal450 said:

Nah, not at all a biggie - I just thought I'd mention it in case you were unaware

I was unaware, and I'm glad you mentioned it. It could be a major issue on sites that use Category Restrictions / Roles.

This did turn out to be a bug in the wp-admin javascript - described here.