lock probs, implicit "update statistics for procedure .." ?

Whe recently sometimes get lock problems at one of our customers. We found out, that the system tables sysprocplan and sysdistrib where locked by a db session started by our application. But from our application we do not execute a "update statistics". Is it possible, that the engine executes something that locks the tables mentioned above ? We entertain suspicion that a stored procedure which is used inside of an select statement causes the trouble. But the problem is not reproducable so far. OS is SunOS 5.8 (Solaris 8), Server 7.31FD5. regards - Frank