-- So when Control is held down, no tags can be selected at all, is that correct?
That's right.
-- If you select a tag, without control held, and click a different one with it held, does the first one become deselected, or does nothing happen?
The first tag becomes deselected.
-- Does Deepdwn stay focused when you do?
Yes, you mean that the window doesn't change to another application, right?
-- If you click a selected tag while control is held, what happens?
Nothing.
-- Do you have any other apps that might be interfering with Ctrl+click?
Not that I am aware of. Is there a way to check?
-- Are you using an external keyboard?
No.
-- Can you tell me what you see when you click the button here with Control held? With Command?
https://cdpn.io/billiam/debug/bGoaGJw/LDAmdnYmeyxr
Unfortunately, the link seems to have expired. It says "This debug view expired."