Answer:

Mercalli offers matching profiles which meets various requirements and several applications.
It now appears that if a wrong profile has been used for a special stabilisation, following effect can appear:

See Image #1:
Original-Video, just a camera panning

See Image #2:
In this case the Profile "Tripod: simulate almost stationary camera" has been used for stabilisation.
The mark on the picture helps to understand that the mountaintop now is stationary.
But now, Mercalli removes all movements, but that means that the complete panning will be removed too!
To solve the stationary cam, the whole view needs to be moved continiously.
As more the picture is moved, as more free area will be shown (here red marked for visualisation). The outcome of this is the impression that the display detail scales down continiously.
What was the misdo or misunderstanding by the user? Simply the use of the wrong profile!
A stationary camera (without rotation) doesn´t match to a record of a panning camera...

See Image #3:
As Image #2, but with the additional active option "fill up border region". Now the border area will be filled with the border colors of the videoclip. Further to this a blurring will be applied. The outcome of this is the impression of an intensive blurring-effect.

Recommendation:
In this case just choose a proper profile for a camera panning, such as "shoulder cam:improve camera panning", because this match the original footage most. The panning will exist furthermore, the camera rotation will be harmonised and all in all the clip will be more perfect - without borders and without blurring.