Why is our IFS Notes subdirectory getting temporary files?

Our IFS subdirectory for Notes/data keeps getting s*.tmp, s*.dtf, id*.dtf files. I delete them, but they keep showing up and they are growing daily. Why are they being created, and is there some setting I can use to stop them?
These are temporary files built during the indexing process. They can be removed, but it is suggested by IBM that you stop the server prior to deleting them. They seem to be version-specific. I've seen people say they were there in 6.01, disappeared in CF2, reappeared in 6.02, then disappeared in 6.0.2CF1.

This was first published in August 2004