Hi Rouslan,
I'm trying to debug a case where clicking on SQL does not bring the SQL panel. Firebug shows me that the call to db_sql.php returns a null value in message.
I found how to trigger this behavior: having a public bookmark whose label contains a character like "é". This server runs PHP 5.3.25.
I think it happens because json_encode() is not happy with the content. I have read on http://php.net/json_encode that this function expects string data to be UTF-8 encoded.
I have tried to use utf8_encode() on the results of $this->_getDisplay() before assigning it to $this->_JSON['message'] but it produces mangled HTML on my SQL page.
Any hint?