Official comment
Hey Simon, glad you're enjoying the update!
As the database and sorting refreshes after each field change (because it's written after you exit the field edit), that will happen. You could open the info pane (to the right) and make all the changes with that song selected, but it will change the position of that track within the collection if any changes made affect the sort.
The font size request has been made by several users and we've passed those requests along to the rekordbox team, hopefully we'll see an option to change it soon.
I know they're still making improvements to the MIDI mapping features but I didn't realize that was missing until you noted it! I'll pass that along. Thanks for the feedback.