Steps to reproduce:
- Open a random page
- Edit source
- Add &ooui=1 to the url
- Click show preview
OOUI design is switched back to old one after showing preview
User (or probably better gadget dev) sometimes need to know if some gadget will work after previewing a page
Note: Feel free to close this as not planned, because OOUI will be deployed soon and the &ooui=1 functionality will be removed after that.