Hello..
I recently discovered that when someone posts a message it appears twice or more (in a single post not doubled).
Editing the post I can't see the extra lines but in the preview the problem appears too.
In the source code the message code is generated more than one times.
For example I type Hello World and I hit post. The message appears like that

Hello World

Hello World

with an extra line.
Are there any ideas how to fix it or someone with the same problem?