Frontend theme bleed into the backend theme

Problem/Motivation

The entity display page (like admin/structure/types/manage/page/display/teaser) contains css from the frontend theme when the entity is rendered as a component.

Steps to reproduce

1. put em { color: red; } css rule into your frontend theme
2. on a entity display page, like admin/structure/types/manage/page/display check "Render using a component"
3. Select a component
problem: an ajax reload happens and the help text contains words in red color.
after save and page reload the text is still red.