in 4.0.x a HtmlEditor inside a panel with layout = fit would stretch to the width of the layout. Now the table and cell containing the HtmlEditor body does have width = 100% by default but the editor itself is only as wide as its toolbar, which is in this case some 276px (don't know why this number exactly). Setting the width property of HtmlEditor has no effect.
Is this a bug, or is there a change in some layout settings necessary? So far I haven't figured out a thing.