When I open a file with .md extension, the filetype is set to markdown, as expected. But the ftplugin for HTML is also loaded as I can see since I have some insert mode mappings in there to auto-insert html entities in place of umlauts. I opened ftplugin/markdown.vim and found this runtime! ftplugin/html.vim ftplugin/html_*.vim ftplugin/html/*.vimsetlocal comments=fb:*,fb:-,fb:+,n:> commentstring=>\ %ssetlocal formatoptions+=tcqln formatoptions-=r formatoptions-=osetlocal formatlistpat=^\\s*\\d\\+\\.\\s\\+\\\|^[-*+]\\s\\+if exists('b:undo_ftplugin')  let b:undo_ftplugin .= |setl cms< com< fo< flp<else  let b:undo_ftplugin = setl cms< com< fo< flp<endifAs you can see, I already commented out the first line. But vim still loads the html plugin. How can I influence this behaviour?
Why does Vim load unrelated ftplugins?
filetype;plugin system;filetype html;filetype markdown
Vim already comes with Markdown support so what happens is that you have two Markdown ftplugins doing the same thing. Since you fixed one (~/.vim/ftplugin/markdown.vim) without fixing the other ($VIMRUNTIME/ftplugin/markdown.vim), your fix is simply overridden by the built-in ftplugin.If you insist on disabling HTML support in markdown buffers you can simply fix the built-in ftplugin (and probably get rid of the extraneous one) but I'd suggest you reconsider your strategy. HTML is valid Markdown so yeah, HTML has its place in Markdown.