A few days ago, I posted an article on my site. It goes smoothly as planned. I finished another article and I tried to save it in another category. What happened next surprised me. I've tried ticking the box of the category but after saving the draft, it goes to the default category(Uncategorized). Tried several times to save it but nothing happened, just goes back to the default category. I tried disabling the plugins but no avail.
Any ideas on what's the problem?