Categories Widget Nesting Weirdness

I am having trouble with one of the sidebar items on my page, powered by the WP Categories Widget.

You will see two sections: Locations – Correct and Locations – Incorrect.

For some reason, as soon as I hit 21 or more posts within that menu, it no longer nests the children items. The ‘correct’ version shows exactly 20 items, and as soon as it displays more than that, as in the ‘incorrect’ version, it shows a flat structure.

What on earth would cause this? I looked through the plugin php and there’s nothing set about a max number, and I can’t think this would be a style problem. Any help in the right direction appreciated.

And yes I’ve contacted the plugin developer and no response. ??

The page I need help with: [log in to see the link]