I think that this is standard behavior in rendered HTML. (At least I think it’s not something specific to Aurelia.) If a container’s content is resized (like collapsing certain regions in it), the scrolling position might be adjusted so that the content neatly fits into its container again.
I think it would be pretty difficult to avoid that automatic scrolling behavior without seeking refuge to hacking and quirking practices (like setting fixed or calculated margins/paddings, setting fixed/calculated container heights, or manually adding whitespace or empty elements to the container’s content).
Perhaps it might be an idea to accept this behavior and use some additional CSS styling for the clicked/focused item (setting a background color, or a shadow, or …) so that it can be easier seen in the (scrolled) list?