strange page-up behaviour with long lines

[erf]

I experience some strange page-up behaviour using Ctrl-u on the attached datapackage.json file. It seem to happen if you scroll below the documentation item, which has a long line of text, and try to scroll up. It seem to work fine if you can see the whole text, but if you make the terminal window smaller, then go below the documentation line, and try to scroll up, it stops and scroll only one character at a time.

datapackage.json.zip