This appears to be a little bug for SafeCraker 2.0 when using it with Wygwam 2.3.1 and Matrix 2.2.1 custom fields.
Simple example:
{field:custom_matrix_field}
produces this output:
<div class="matrix"></div>
whereas it should be:
<div class="matrix"></div>
Haven’t tried Playa, so dunno if there’s an issue there too.
Other tags like <fieldset> and <div> seem to wrap properly around those fields.