It's there since 9.5, don't use Quick Link feature as it can harm your projects.
Basically, if you have collapsed folder tracks, Cubase does not automatically deselect tracks that are inside the folder. It acts like if you hold CTRL+click and select several tracks.
Steps to recreate
01 create 3 audio tracks
02 place two of them into the folder and close it (folder)
03 on the Mixer Console select (click) on the any of the tracks within a folder
04 on the timeline view click on the track outside the folder
= both tracks are being selected. and if you have Quick Link enabled you gonna be screwing your project by making changes to both these tracks (or any numbers of tracks that are highlighted.
