i just noticed that little bug and im gonna write it here to remember it and fix it later.
i wanted to create a post in a folder that only had 1 post in it. but accidentally created my post on the root. so i just moved it in the folder that i wanted to post it in. but then i noticed the folder was still saying it only contained 1 post. when i looked in the folder though the 2 posts were there.
this error will be fixed soon but is not really a big problem. also as soon as a new post or folder is posted in that folder, the number of posts or folders gets recounted from scratch so the error does not stay long.