Start up Libre Select File --> Open Click on "All files" The resulting list of file type has a huge area of white space at the top.
This is a GTK dialog. GTK lists have such behaviour.
It looks very peculiar. I hadn't even noticed the arrows top and bottom. On using the bottom arrow the text goes up into the white space until it is filled. Please consider the following before completely dismissing this bug: Reduce the overall height of the control, on a 1920x1600 display it looks frankly ridiculous as it expands the entire height of the display! Fill the list to the top at the outset, Choose a different GTK control, I have not seen another open file dialog that uses this control.
This is not a bug. If anything, it's a GTK bug, you might report it in their bugtracker.