In my development environment scheduled posts are published without any problem. Are there any plugins on your site that deal with scheduling posts?
Edit: I’ve tried this on a live site as well. It’s working, but I noticed a strange behaviour when the ‘Auto Publish’ setting is not enabled. For some reason when a scheduled post is saved the ‘Publish Post to Discourse’ meta-box value is not updated. This means that if a post is scheduled and then later updated, it will loose the ‘Publish post to Discourse’ value. I’ll sort this out right away.