Thanks again to Viktor for spotting this issue!
I've launched leo-web version 1.0.19 to address it. I've worked on the system clipboard handling and have hopefully solved the issues that could arise when the browser's permissions prevent proper clipboard usage.
If the required permissions are missing when clipboard access is needed, a message dialog will now appear the first time this occurs during a session.

Here's what following those instructions would look like in most browsers:

Please try it out and let me know if you encounter any issues — clipboard-related or otherwise! :)
Félix
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I've launched leo-web version 1.0.19 to address it. I've worked on the system clipboard handling and have hopefully solved the issues that could arise when the browser's permissions prevent proper clipboard usage.
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