Hello,
As the title states, when you create a text input inside of a modal view, the background image is undefined. This does not cause any functional issues however it is annoying that requests are made for undefined on each load of the modal view. You can see the issue in your mobile modal demo at https://demos.telerik.com/kendo-ui/m/index#modalview/index. Open the modal view, inspect either of the text inputs and you will see the background-image points to an undefined url.
Thanks,
Matt