Path for image upload in subpages is wrong

If a user uploads an image to the "home" subpage in a challenge, the file is being uploaded to the main storage folder, but the URL that's added to the Markdown content contains a foldername from the current subpage.

E.g. This path is added to the Markdown:
https://innovation.fabcity.hamburg/home/storage/challenges/92wYmj7vZOK9fFS8ATUvj8Cua6w2xY8m37BVGqXe.png
This is the actual, correct path:
https://innovation.fabcity.hamburg/storage/challenges/92wYmj7vZOK9fFS8ATUvj8Cua6w2xY8m37BVGqXe.png

Also deleting these images won't work – probably because of the same reason.