Right now nothing happens, which is probably not ideal.
We have three different requests:
- Focus the existing Spectacle window: https://bugs.kde.org/show_bug.cgi?id=399760
- Start a new instance of Spectacle: https://bugs.kde.org/show_bug.cgi?id=374770
- Take a new screenshot with the current parameters: https://bugs.kde.org/show_bug.cgi?id=383897
None of these seems like an inherently wrong outcome, so perhaps we should have a global option and support all three, defaulting to one of them.