I'm using HeidiSQL often in a MySQL table with a primary key which is spanned over 3 columns.
When I duplicate one row, the primary key columns are not duplicated to the new editable row. I can imagine why, but in my case I often have to change one digit in only one column. Actually I have to fill the three columns manually because I cant leave the row to copy the values from the origin row. As a workaround I export the row(s) as SQL and make my change in the SQL editor before executing.
For this case it would be nice, to get a preference-checkbox (or something else -> a new [full]duplicate command; shortcut;...) which enables to duplicate the (primary/unique) keys as well. Theoretically it should possible because the row will be saved only if I leave the row (and changed the value of course).
I would be glad if this request will implemented :-)
(I moved from SQLyog months ago, there I had that feature but I'm using HeidiSQL now because of many other features)