When the Windows single-line editbox becomes full it treats that as if a return key has been pressed and clears the editbox. Some versions ago I placed a limit on the number of characters that could be typed into the editbox to prevent the above problem. However the limit also prevented users from pasting multiple lines into a single-line editbox, eg. in the case where they wanted to send several separate lines into a channel or query window. So the limitation was removed to permit this.