I have user reference field that gets is potential references from a view. The label field being returned is from a Name field and even though I have it set to render in plain text and add no default classes, I'm still getting html wrappers so its being returned as
<span><span>First_Name Last_Name</span></span>

In the multiselect widget, the html is being stripped from the available options but not from the default value.

I chased this down to multiselect_field_widget_form(). It calls _multiselect_build_widget_code($options, $items, $element, $required) which modifies $options to have html stripped.

However, since its not passed by reference multiselect_field_widget_form() doesn't see the modified options. I'm not sure of the interaction between _multiselect_build_widget_code and the returned element from multiselect_field_widget_form() but changing the declaration of _multiselect_build_widget_code() to

_multiselect_build_widget_code(&$options, $items, $element, $required)

ensures that the both the selected and unselected lists have no HTML in the labels.