Here is what appears to have "cured" the problem: I re-opened the current log file that was exhibiting the problem and found that the problem was still present.
I closed and reopened DX4WIN. The file now sorts normally! There appears to have been a partial corruption that did not disturb most normal program operation, but which reset when the application was cycled. I suppose that to programmer types that is an obvious thing to try first before asking for help, but it was non-obvious to me. I would still like to understand what happened. Garry, NI6T
