Please see secure note. As soon as I add a grid element to header or footer, the editing is impossible due flickering.
EDIT: I figured out that as soon as I add an element with an effect like transform at interaction to a cell in a grid, the flickering starts.
To make myself clearer: Text element shall transform at mouse over. And there is an initial effect like scew on text element as well. As soon as this is inserted into a cell, boom.