We began our research
In mitkDisplayInteractor.h
in the method:
void mitk::DisplayInteractor::ExecuteOperation(mitk::Operation * operation)

Here a render function is called:
renderer->GetDisplayGeometry()->ZoomWithFixedWorldCoordinates(factor, dcOperation->GetStartDisplayCoordinate(), dcOperation->GetStartCoordinateInMM());

The error must be in
bool mitk::DisplayGeometry::ZoomWithFixedWorldCoordinates(ScalarType factor, const Point2D& focusDisplayUnits, const Point2D& focusUnitsInMM )

The first parameter "factor" is correct. The other paramters should be checked as well as the calls in this method.

Bug could not be reproduced on my PC (but it is quite hard to measure unbiasedly whether zooming accelerates when closing the project and opening the same image).

The source of error could be in function vtkPropRenderer::AdjustCameraToScene() as well, where a "zoomFactor" is set.

We were unable to reproduce the bug.