If you type not a link text into “link from the web” field of the image upload page in mobile web then you could see something white and weird in the center:
After splitting the keyboard you could see that this is a tooltip:
I’m not sure whether this is a site or a browser/OS issue. Let the developers decide. I would like to see that tooltip in the visible area without a need to split a keyboard.
Tested on iPad in Chrome/Firefox/Safari.