Rotation Problem (with Video)

Hi!
I’m working on a Compositing Tool. The UI is mostly done with sliders.
The tool got a Camera, which can be rotated around all 3-axis with the sliders.
After that, there should be the possibility to rotate the “final picture” between -90 and 90 degrees. Again with a slider.

My Idea was to go the hierarchy one step down and use an empty actor that holds the camera.
So for the rotation of the final picture i need to rotate the empty actor around the optical axis of the camera…
Here my BP Setup:

This works fine as long as i use small angles, the Forward Vector of the camera isn’t changing like supposed. If i move the slider to the end, it goes crazy and the Forward Vector changes to strange values. And it even the Angle doesnt change at the end of the slider, as long as i move the mouse it calculates a new Forward Vector for the camera…

Moving the slider fast forwards and back at a relatively high angle value cause the same error…
Take a look at the video:

So I’m not sure if this is a bug or a thinking error of me… Anybody got an idea for a solution to this or a workaround?