Copy a content in one lang in another lang render temporarily this content in the content in the wrong lang

Cf general use case, parent JIRA

In the current scnario my destination site has DE lang as default + I added EN. Then I copied the "How to use this demo" boxlet from the default ACME (in EN) to the empty home of this site (in DE) on an activable area.

The boxlet is copied and the EN content from ACME is displayed on the DE lang on my newly created site. When I refresh the page such a content "disappear" (from a visual point of view) and is correctly reassigned to EN.