Horizontal scrollbar doesn't appear until scrolling down

Stash pull request in diff mode. Text is wide enough necessitating horizontal scrolling. For some reason the horizontal scrollbar doesn't appear until scrolling down a bit (see attached). Thus in order to scroll right, I have to first scroll down then to the right, very cumbersome. If there's clipped content, the scrollbar should always appear (without the user have to do additional scrolling in the tangental direction).