Scrolling wrong panel

I'm trying to use this library, but it seems to sometimes scroll the main content panel, not the nav panel. This issue is present on the demo site.

To reproduce:

1. Open https://slideout.js.org/ on mobile in the latest version of iOS Safari (I'm on 11.1)
2. Make sure the window is shorter than the menu content. This is the case for me on an iPhone SE in landscape.
3. Open the menu. Tap somewhere in the content area. Now try scrolling. The content will scroll instead of the menu, making the later menu items inaccessible. It's possible to regain focus on the menu by tapping carefully, but it's not simple.