To the best of my knowledge, log pruning occurs only when you start the
scheduler. I can't speak to what you've seen with OS/2.

When this feature first came out (I think it was with level 0.6 of the
clients), I was thrilled, since the logs can become real space hogs.
Imagine my disappointment when I found that it occurs only when the
scheduler is started! I opened a problem with IBM; their response was
those three words I can't stand: "working as designed".

I felt very strongly that the design was defective, since in an unattended
environment, it either renders the feature useless, or takes the
"unattended" out of "unattended backup", depending on whether you wanted
to stop the scheduler and restart just to prune the log.

Anyway, IBM got enough complaints that in the next version, they will
change the algorithm to prune logs after a scheduled event completes on
the client.