I just discovered this myself while trying to reduce real-time peak spikes. Whenever I highlight an Instrument track with record enabled, I get fairly severe real-time peak spikes. If I simply switch to an audio track (with record enabled or disabled), or disable record on the Instrument track, the real-time peak meter drops to almost zero! So, I unticked the “Enable Record on Selected MIDI Track” setting and now only enable record on Instrument tracks when I need to.
Thanks for posting all this info; it’s useful to know that this is not a problem specific to my system, but rather a problem with Cubase. Cheers…