How to prioritze a backlog in a multi-level agile board

We have created our issues as a hierarchy of Epic -> Feature -> Product Backlog Item -> Task. Our Development Board uses "Product backlog Item" as swimlane type. The board look as expected.

But when we try to prioritize the backlog from the agile board view, the backlog uses a tree-view structure including all hierarchy levels (from Epic down to Product Backlog Item). Epic is greyed-out, since it is excluded by the underlying saved search for the backlog.

The problem is, that we cannot prioritize individual "Feature"s independent from the "Epic"s. If we try to move a "Feature 1" from one "Epic 2" after a Feature from another "Epic 2", the "Feature 1" becomes a child of some other Epic. THis is probably due to the fact that Epics are visible in the backlog view.

I wonder now, what I might be doing wrong or whether such multi-level project setups are not supported by YouTrack.

Any help yould be highly appreciated.

Cheers,
(Bernie).