Sorting 100+ files in one directory creates wrong sequencing

[taylorren]

In config.yml file, I have modified as below:

collections:
  posts:
    output: true
    permalink: "/:path/:basename.html"
    sort_by: 'slug'
    sort_type: 'ascending'

Under posts/ directory, I have created a sub-directory called wesley and it contains 100+ (131 to be exact) files: 0.toc.md, 001.md, 002.md, ..., 131.md. For each of these files, I created the header like this:

layout: "post"
title: "钻石花"
slug: "wesley-001"
book: 卫斯理全集

The above 001 will be corresponding to the deemed sequence of the output. In other words, the correct sequencing should be 0.toc, 001, 002, ...131.

However, when the site is built, and I view the post list page, the first file in the sequence becomes 122.html. After reaching 131.html, it will display 0.toc.html and 001 onwards till 121.

I have other sub-directories under posts with similar slug naming convention but don't have this behavior.

Don't know what is the problem for this. Please help.