From https://bugs.launchpad.net/catfish-search/+bug/1559040 Firstly I've reported this bug to gtk bugzilla, but it's not their bug https://bugzilla.gnome.org/show_bug.cgi?id=762775 Horizontal scrollbars prevent access to lowest element. Some themes has hor scrollbars higher than entry
Sean Davis referenced this bugreport in commit d5228260f98f4d4f5fcae92cca0f2617972d39c4 Disable overlay scrolling (bug 14487), bump minimum gtk to 3.16 https://git.xfce.org/apps/catfish/commit?id=d5228260f98f4d4f5fcae92cca0f2617972d39c4
There's not a great way to handle this bug outside of adding bottom margins to the results list or disabling overlay scrollbars. Since the former option looks pretty bad, I've gone with the latter.