I have similar problem. Also, the "Watchdog has expired. Target detached" errors appears with completely disabled watchdog timers too.
For example, in next code block
if ((*dialer_status) == (*prev_dialer_status))
// If the ppp state machine takes more than 30 seconds to complete dial, report error.
if(++dialer_timeout >= 600)
result = -1;
*prev_dialer_status = *dialer_status;
this error appears after 11 calls of tx_thread_sleep(). The 12th call of this function will cause detaching from target.