Version:            (using Devel)
Installed from:    Compiled sources

1-Launch plasma-desktop when you've only 1 screen. 
2-Add a new screen extending your desktop.
3-Open to the button in the corner.
4-You'll see that the ToolBoxActions are duplicated.
If you repeat this more than once, the number of ToolBoxActions will be exponential.

I've tried to fix this, but I don't have enough time to understand how it works :( but I can write here some technical things that may help.

Flow inside the code:
1-When a new screen is added, checkScreens-->checkScreen is called.
2-checkScreen have a few conditionals, which emit containmentAdded signal whatever the containment already exists or not.
3-Then, PlasmaApp::containmentAdded is called because of the signal, and this function add the ToolBoxActions.

The error: If the containment already exists, and already have actions, they will be duplicated.

I tried to create a new signal "existingContainmentAdded" but it produce some odd behaviors, so I stop my research here.

Thanks!