The cause for this was that the `HandleMouseInput` method of the `EditorViewPortController` ran before the one from the regular `ViewPortController`, thus intercepting the button press.
Switching the order of the two around fixes that, but introduced another problem, namely that the tooltips stopped working. Switching the order meant that the `ViewPortController` laid "on top" of the `EditorViewPortController`, so the latter didn't receive the `MouseEntered` event anymore. Setting the `IgnoreMouseOver` flag in the `ViewPortController` fixes this.
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