Not sure if this is a minor bug, or an opportunity for a suggestion 
, but here goes:
In the MIDI Assignments display, if I create an Assignment for a Controller to a Rack’s Gain, the mapping appears in the Options column. And it does get saved. But when I come back to this display (say after switching to a different song), the Options display is blank. The values are retained, but not displayed unless I click on that area to edit them,
I haven’t tested different kinds of Assignments, only Controller Events -> Rack or Plugin Gain settings.