Unassign click handlers from disabled mover buttons

editor/block-mover/index.js

@@ -15,17 +15,22 @@ import './style.scss';
 import { isFirstBlock, isLastBlock } from '../selectors';
 
 function BlockMover( { onMoveUp, onMoveDown, isFirst, isLast } ) {
+	// We emulate a disabled state because forcefully applying the `disabled`
+	// attribute on the button while it has focus causes the screen to change
+	// to an unfocused state (body as active element) without firing blur on,
+	// the rendering parent, leaving it unable to react to focus out.
+
 	return (
 		<div className="editor-block-mover">
 			<IconButton
 				className="editor-block-mover__control"
-				onClick={ onMoveUp }
+				onClick={ isFirst ? null : onMoveUp }
 				icon="arrow-up-alt2"
 				aria-disabled={ isFirst }
 			/>
 			<IconButton
 				className="editor-block-mover__control"
-				onClick={ onMoveDown }
+				onClick={ isLast ? null : onMoveDown }
 				icon="arrow-down-alt2"
 				aria-disabled={ isLast }
 			/>