If you disable the pinning of the vsti window in the instrument editor, and then detach the instrument editor, no vsti will open anymore, if you double-click the instrument entry.
Ok, here is the exact steps to reproduce (macos 10.14.6 here):
- Detach instrument editor, load vsti into slot
- Disable pinning
- Close instrument editor and vsti window
- Double click instrument slot. Only instrument editor appears. On second double-click, the vst window now appears. Maybe this was intended, but at least I would expect the vsti window on any double-click.