Bug? MS-Forms background image lost when you scroll down

I have a Microsoft form with a background image - see here: https://forms.office.com/Pages/ResponsePage.aspx?id=G96VzPWXk0-0uv5ouFLPkSRcml1ztjVNg-miBzh8WidUNVQ1S1dPMlZKMEVFRjRUTTgyVDhQQjJLNC4u   T...