External MIDI control display anomaly

[Almost Aviation]

I have set up some buttons on my Korg nanoKONTROL 2 to switch between Drone types (middle line on the Drone display), which works fine. The changes are reflected on the display reliably, but the middle line always goes yellow, even if the NDLR is set to the Position (top) or Trigger (bottom) line. When this happens the NDLR has two lines highlighted in yellow instead of one. This is a visual thing only, it stays in the correct mode (so, for example, if I had set Position mode, the knob still changes the Position). I don't think this is a refresh problem, I wouldn't expect it to change the colour at all.

Hope this makes sense. There may be other similar glitches, but that's all I've tried so far.