Muting vst 2 plugin on mono channel mutes whole track

I’ve discovered a weird behaviour in Cubase 8.0.3 running on a MacBook Pro, OSX Yosemite 10.10.5

On a mono audio track, a mono VST plugin (VST 2) that is muted with Cubase mute function will result in the whole track being muted. A stereo or VST3 plugin will not do this, and it is very confusing why a mono VST 2 plugin result in this.

This is happening with Fabfilter plugins (Pro Q 2, Pro C 2) as well as Blue Cat Audio (BC Gain 3). I guess all mono VST plugins will create this issue.

To reproduce:
Create mono audio track
Load a mono VST plugin
Use Cubase mute-function on plugin - it will result in no audio going through plugin.