I've managed to reproduce something similar only on audio tracks, and only if they're empty.
It's as if Qtractor detects the possibility of receiving audio to update the plugin UI.
It might be related to automatic plugin disconnection, and perhaps it is a small bug... I'm not sure.
On the other hand,
If the plugin is deactivated, logically the changes aren't visible; I think that's to be expected.
I've checked the following.
I've managed to reproduce something similar only on audio tracks, and only if they're empty.
It's as if Qtractor detects the possibility of receiving audio to update the plugin UI.
It might be related to automatic plugin disconnection, and perhaps it is a small bug... I'm not sure.
On the other hand,
If the plugin is deactivated, logically the changes aren't visible; I think that's to be expected.