RSS pubDate and the lastBuildDate different

I am having issues with MailChimp not publishing a RSS-generated campaign as expected.

MailChimp says that the “pubDate and the lastBuildDate are different”, as well as the Facebook post date (using a FB plugin to post to a a FB page.

The following thread refers to something in WordPress 2.5, and is 6 years old. (http://wordpress.org/support/topic/resolvedrss-feeds-showing-the-wrong-date?replies=1″)

Is the solution still current? Is it a Theme issue or is it a WordPress issue? Is there a plugin that’d fix this?

Thanks,
Peter