Where in the vim script is "+-- N lines: " added to folded markdown headings?

I am using vim 7.4 with
markdown heading folding from https://gist.github.com/vim-voom/1035030
and highlighting from /usr/share/vim/vim74/syntax/markdown.vim

With this setup, folded headings are preceded by "+-- N lines: ", where N is the heading level.
Unfolded headings are rendered as is.
This causes folded and unfolded headings to misalign.
In this example, heading3 is unfolded:

+-- 37 lines: #heading1

+-- 85 lines: #heading2

#heading3

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.

+-- 16 lines: #heading4

Where in the vim script are the "+-- N lines: " added to the folded markdown headings?
I would like to change the vim script so that folded and unfolded headings align on the left, something like this:

#heading1 :37 lines

#heading2 :85 lines

#heading3

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.

#heading4 :16 lines

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