Thank you Jimmy57 - diagnosis was perfect. Took door panel off and found chafed wire, probably touching regulator arm as window descended. Taped and secured wire. Problem solved. Thanks again.

1998 S90 drivers window triggers central locking only when window is being lowered continuously. I am able to defeat the symptom by lowering window in small amounts incrementally. Locking is not activated when driver window is raised and no other windows activate locking at any time.