A few minutes ago when I was writing a post in thread of Jambler.io, and during the preview I got the error, "No subject was filled in." Although, in the screenshot that I'll share below, the subject was selected automatically as it was a reply in a topic but still that error was present.

As you can see in the image that the subject is already filled but still I got that error. I hope that admin/president of the forum will find a solution for this error. I created this thread to report the error so it can solved, and I hope that it will catch the eye of the admin so in free time he might fix that error.