Yup, I see the same behavior, I have resolved the bug for the next release. In the meantime you can edit rpr-admin-menu.php line 209 from:
<td align="center" style="padding-top: 0px; padding-bottom: 0px;"><input type="checkbox" name="required_fields[]" id="required_fields[]" alue="about" <?php if ( is_array( $register_plus_redux->rpr_get_option( 'required_fields' ) ) && in_array( 'about', $register_plus_redux->rpr_get_option( 'required_fields' ) ) ) echo 'checked="checked"'; ?> <?php if ( is_array( $register_plus_redux->rpr_get_option( 'show_fields' ) ) && !in_array( 'about', $register_plus_redux->rpr_get_option( 'show_fields' ) ) ) echo 'disabled="disabled"'; ?> /></td>
to:
<td align="center" style="padding-top: 0px; padding-bottom: 0px;"><input type="checkbox" name="required_fields[]" id="required_fields[]" value="about" <?php if ( is_array( $register_plus_redux->rpr_get_option( 'required_fields' ) ) && in_array( 'about', $register_plus_redux->rpr_get_option( 'required_fields' ) ) ) echo 'checked="checked"'; ?> <?php if ( is_array( $register_plus_redux->rpr_get_option( 'show_fields' ) ) && !in_array( 'about', $register_plus_redux->rpr_get_option( 'show_fields' ) ) ) echo 'disabled="disabled"'; ?> /></td>