Why does a multiple choice field with log entries enabled not retain it's value when record is edited?

If you still want to use that field type, you can use a form rule to only make it required if the field is blank. I be ie I�ve that should make it non required after its first entry,

Let Ken know if you need help with the Formulas to parse our the elements of the most recent update.

An alternative is to use an Action to log changes, either to a child table or to a field set to log changes.