Selecting editor by left-clicking also activates text selection

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I have a weird issue: Whenever I select the Wing IDE editor window by left-clicking on it, I am automatically in a text selection mode. When I move the mouse, the yellow area shows what I am selecting. The only way to stop it, seems to be to left-click somewhere in the editor window again. This doesn't happen when I Command-Tab to the window.

I have had this for a while and was sort of ignoring it, but I would like to turn it off now. Because of my ignoring it, I am not sure if it was a Wing update or macOS Catalina. This behaviour does not occur in any other program I use.

Is this a setting I can change or something I am not seeing here?

Thanks, Jan