I have the following mystery with an AIX 4.3 system:

The machine runs an application that consists of several processes.
They are all started as background processes by a shell script, which
then exits. The processes keep running indefinitly. Some of them run
setuid root, others run as regular user processes.

One of these processes is "cleanup". It sleeps most of the time. Once
every few hours, it wakes up, searches certain directories for old
unused files created by the other processes, and deletes them. (Using
readdir, stat, and unlink). "cleanup" does not have root privileges.

Sometimes, when "cleanup" wakes up, the entire application gets killed.
I'm not even sure if it can be considered a "process group" at this
point, since the parent-process-id for all of them is 1 (init). But
all of the application processes get killed at once. All other
processes on the system continue to run unhindered.
I can't find anything in any system log to explain why.

Does anyone here know what "cleanup" might be doing that offends AIX
4.3 so badly it kills not only "cleanup" but all its siblings as well?