1. Edit core/admin_templates/promo_block_groups/promo_block_group_edit.tpl - add empty_label="la_Yes" attribute to the $prefix_PredefinedOptions tag (used for custom TransitionEffect field display).
2. Go to Website & Content -> Promo Blocks section in the adm.console.
3. Open "Default Group" for edit.
4. Click on "Promo Transition Effect" dropdown.
5. Confirm, that first value in dropdown is displayed as "Yes", not "!YES!".