Well, I found it. I'm holding many of my tables open in the default data session. New records are added in a VFE-codebook form which uses a private DS. One of the tables that has been failing is called RSTYPE. If I don't open this table in the default data session, I don't get the bug. If I do, I do.

Does that ring any bells for folks?

Food for thought: I keep 17 tables open in the default DS which are also used by forms including some of the most active tables but I've seen this problem with only 5 of them.

Peter