heading syntax hilighting doesn't "trace back"

[lerouxb]

I've been getting this problem with all the different vim markdown plugins I tried:

If I type a heading, then the line below it add ==== to make it a heading, the heading and the line of = chars doesn't change colour until I make a change in a line above the heading (like insert a line break). If I then remove the line of = characters it doesn't clear the heading color again until I do the same.

I have seen an intermittent issue like this in another plugin before, so I learned all about the various syntax sync options.

If I run ":syntax sync" I see lots of things, so I figured it might be things interacting strangely. So I ran ":syntax sync clear" followed by ":syntax sync fromstart", but it makes no difference.

I have even upgraded my copy of macvim. After that I tried in my copy of vim in the command-line and it behaves the same too, so I doubt it is that.

Is there something I'm missing? Why is it that for me the markdown plugin can't even be forced to always re-evaluate all the syntax?