It's true the Patch panel VCA hold the last value that's put into it, when you disconnect the VCA input like you do. That no matter which modulator you have in the input i believe.
When you restart the Synth, then the signal go away.
However - there is no reason to have the VCA output connected to anything, if you disconnect the VCA input. So it only matter, if you keep working, with a connection you don't use, unless you wan't the effect it give, while you are in a session untill you restart the application.
I don't know, if the original hardware have the same behavior.
At worst it's a bug, that while it's there easyli can be fixed by the user, by disconnecting and remove something that's not in use anyway.
But stricktly then yes - if it's a bug, then any kind of bug is a bug.