Shared Clipboard stops working

[whoami]

Host: Windows 7 x64

Step 1: Start guest with guest additions, bi-directional clipboard (in my case, linux mint)

clipboard works both ways, as it should.

Step 2: Start another guest without guest additions, clipboard sharing disabled (in my case, windows 10 preview)

clipboard does not share in 2nd guest, as intended; however, clipboard no longer is shared in the 1st guest now, either direction.