i found a bug which correspond to Fix #2531090 (Editor class)

var ed = new Y.EditorBase(
{
content: '<p>Text goes here'
});
ed.render();
});

then I mark the "goes" word and clicking on the "Bold" button from the toolbar
(until now everything is ok)

now I go to the end of the line and trying to erase the "here" word with "backspace" key.

On Safari, after clicking on the backspace button, Editor lose focus.
On Chrome, the cursor jump to the "goes" word after one click on the "backspace" key.