clipromtlines not working in 2018?

I had a user who didn't anchor his command line, and started having his command history scroll completely across his screen. I told him to reset clipromptlines to 3 or 4. he told me that was working, but almost immediately called me back and said it stopped working. He can reset it, but it will immediately happen again, plus the current setting is correct.
Can anyone tell what system variable is overriding clipromptlines?

Generally when system variables are changed for no apparent reason a lisp routine is at fault. It may also be getting reset by acaddoc.lsp or a menu lisp (*.mnl file).

Command Line Properties are stored in Workspaces. Has he tried changing Workspaces? They may need modifying in the CUI.