Bug with cover while scrolling

[NR]

Hey!

Really don't know what triggered this bug while working on my website, but since a few days there's a strange problem with the cover feature while scrolling up and down. While going down everything seems to be normal, but when scrolling up the hidden cover image is partially shown.

http://normanreuter.com/

PLEASE HELP! :)

[mariusjopen]

Dear @NR
the website works well here.
Did you solve it already?

Which browser did you use when the problem was there?

Best!

Marius