Hi Christian,
Thanks for bringing this issue to our attention.
This is a known issue. And this issue occurs when zooming done by using mouse. If you zoom the chart using keys it works well.
So we have filed a bug report in our internal defect tracking system. We have requested our developer to provide more information regarding the time frame to fix this issue. Hope we can provide you with more information shortly.
Let me know if you have any more questions.
Regards,
Sureshbabu
Key And Mouse Zooming Sample