Yes, this was the wrong place. The definition of a column with the contents of multiple fields causes irritation if you expect that contents to appear in a single field.
To write back the contents of a column to the named field requires a modification to that field as otherwise you have the phenomenon that you SEE information as to appear in one field but is actually a composition of two separate fields.
No, the best way to merge two fields is to create an action (See FAQs for that)
of the type
"Format value" (see also FAQs for that).
Enter as field name COMMENT
Enter as format string "%comment% %COMMENT _ADD%"
Run once for all the files that do not have the correct comment yet.
And then best delete the field COMMENT _ADD again so that the contents of that field is not merged with COMMENT again.