Incorrect number of replies (it says only 1 person replied, when in the reality 4 replied):
http://www.gog.com/forum/terraria/program_to_view_worlds_compatible_with_13
And I just posted in this thread, but for some strange reason it's invisible, even if I go to this url:
http://www.gog.com/forum/terraria/terraria_1304_plz/post21
It still doesn't works.

It's visible now.

Anyway, I had a new topic I posted in the Elminage Gothic subforum not show up at all (though direct links worked) until I posted a reply to the topic.

No idea why the forum is acting up this way.

Certain threads in the game forums have been displaying incorrect post counts for a month or two now; some threads (such as BillyMaysFan59's Terraria screenshots thread) are frequently unable to be viewed past the first page for a while after someone posts in them.

Not sure what you mean by your post being "invisible" -- I know that once in a while it can take a couple minutes for a new post to actually show up in the thread, and to my knowledge that's been the case since before I signed up for GOG.