Your bug is slightly different. I can select a piano (e.g.) and a folder track. The folder track vanishes only when I move a note, not when I just selct them.
But yes, there is a bug. THIS BUG WAS NOT IN CUBASE 9.5.
In 9.5 I could happily select a combo of single and folder tracks for work in key edit. In 10 I cannot.
This bug hampers me all the time, every 5 minutes. It is so much easier to select a folder track for work in key edit than to go ferreting around for individual tracks. All my time is spent in key edit.