When there is a connection sharing or a phone call on the iPhone, that adds an "incall status bar" of 20 pt to the NavigationBar. If there is a TSMessage during that time, the message is offset by 20 pts down, therefore not "attached" to the navigationBar anymore.

See pictures attached
Picture 1 : table VC (no message)
Picture 2 : table VC with TSMessage
Picture 3 : table VC with TS message with call status bar : oups !!