Sometimes, when double-clicking a plugin in the FX browser, the plugin is added twice: once to the selected track, and another to a “random” track. I presume Renoise is interpreting a slight drag after the double-click as a separate action. Notably this only happens with plugins that take a while to load (a good free one to test is Chow Tape Model).
This happens in Renoise 3.4.4 under macOS 14 & 15.
No, it happens with all tools disabled. Experimenting a bit more, I’ve noticed I can easily double-click and hold, then drag the second plugin copy after the first one has already been added to the mixer. In doing this I’ve also noticed that Renoise is switching between the white Renoise cursor and black macOS cursor while handling double-clicks. I can’t recall experiencing any of this behavior before macOS 14.