Problems often arise when a single port is monitored by more than one process. If a port is used by an enabled service under a ttymon port monitor running under the SAF, and the same port is also monitored by a ttymon process running in ttymon express mode (that is, started by init when it reads inittab, not by sac when it reads its administrative file), then the port will behave unpredictably. You should examine the system for such ambiguously configured ports.