Keyboard focus in VisualEditor starts with the help-link (question-mark icon) instead of the beginning of the editor bar. This is caused by the toolbar being composed of a left and right section, but they are floated "in-reverse", i.e., the "actions"-div is set to "float:right".
<div class="oo-ui-toolbar-actions">...</div> <div class="oo-ui-toolbar-tools">...</div>
To achieve correct tab order, the tools-div should be rendered before the actions-div.