Selecting just the chords or both the chords and the scale makes no difference on the ability to transpose chords on my system. The behavior is exactly the same either way.
Also I’m pretty sure that Root Key refers to both the scale and the chord. The term Root Key in itself doesn’t have any musical meaning but if read as Root or Key it makes sense.
- Scales have Keys but not Roots. Chords have Roots but not Keys.
- If you select just a single chord, and that’s it - no scale, the Root Key field has a value in it. And if you change that value the chord changes. So clearly it is a piece of data stored in the data structure of a chord object - if it wasn’t then that field wouldn’t be displayed when a chord is selected. Compare the available fields on the info line when just a chord or just a scale is selected. They share 2 data fields Start and Root Key but everything is is unique to one or the other.