Every txn consists of the ‘parent’ data and a number of ‘splits’.
Even a single-line txn with one category has 1 line/split.
When you enter a single line txn, moneydance hides the ‘edit splits’ popup (and the memo that you enter becomes the first split’s Description). Actually, at this point there is no way on screen to enter the parent’s memo.
The parent holds no amounts.
Each split holds its own amount for that line.
The parent holds the Description for the whole txn.
The parent can also hold a Memo (but very difficult to actually enter).
Thus the parent’s Description and Memo apply to the whole txn (and all splits)
The split lines can each only hold a Description (for that split line).
The split lines can NOT hold a memo, there is no data field for this.
When you edit splits, the first text field on a split’s line is that split line’s description field. There is no way currently to enter a memo as the field does not exist in the database (despite rather oddly appearing to be an empty useable field.
Another point. If you right click a txn, then select ‘show other side’, you flip to a slightly confusing view and can edit the split data directly. Any field that shows a [bracket] around the field means you are viewing the parent’s data if the split’s data is missing. If you type in this field, and if the split has this field, then you enter data into the split. At this point, the Memo field you can see and edit is actually the parent’s memo that you cannot edit anywhere else.
As for the future, I suppose you would need to request an enhancement.