All the preview sheets that are formatted as a character sheet (rather than a stat block) force a horizontal scrollbar to appear. Generally, the primary culprit seems to be the spell table, though in some sheets the equipment table is also a bit wide. I have no idea what's making the compact sheet have a horizontal scrollbar, since it seems to fit within the window. It makes no difference whether full spell descriptions are enabled.
For reference, my window is wide enough for everything above equipment on the standard sheet to display with no scrolling required, provided the side pane is minimized. When I first opened PCGen, the window was smaller. I realize there's a limit to how much you can cut the width, though.
Unable to reproduce this.