Promotion validation error removes offer details during creation

Describe your bug or feature request.

When creating a new promotion and saving, all promotion details are removed and hidden if a validation error occurs.

If a bug, provide steps to reproduce it from a clean install.

- Create a new promotion
- select "Buy X Get Y" offer type
- specify the product/sku in both the BUY and GET fieldsets
- DO NOT specify the 'amount off'
- Save the promotion
- Validation errors will occur indicating that an amount off (percentage) must be specified.

The error will appear on every field within the offer(s) and the product criteria will no longer be visible.
See Attachment.