Audio Mixdown songs speed changed

Hi all,
I am using Cubase 6.0.7 and experienced an interesting behavior. I wanted to mixdown a part of a song to reuse it as audio track. If I mixdown in WAV format the speed of the song changes, I tested all settings in the mixdown UI. If I mixdown in mp3 format, everything is ok.

Has anybody similar experiences? And what could be the reason for that?

Thanks & Best regards

Ah, I have an idea! I set the project to a sample rate of 48000 and the audio mixdown to 44100. That seems to be the issue…