Hey Christian,
The width / height is defined within the ad itself. There is already a defined width / height on the template but the image itself is rendered as a horizontal image.
The only way to address this right now is to add an overflow: hidden on the module wrapper but this does not fix the real issue because your ad is still not vertical. It's still generated as horizontal as you can see from my screen shot below.
If you want the codes to enforce that anything that goes beyond the width of the module, you could use the following codes,
P/S: I think you should bring this up with Google's support.