Try this...
On the left side,in the modx admin(where all your files are)
1. open up your blog folder(page,file..call it as you like

) you should see your post there as a separate file ( page...)
2. right-click on that file and click publish ( nevermind if its already published

}
3. then refresh whole page, if you’re on Firefox hold shift and then hit refresh, if IE7 hold ctrl+F5
4. repeat step 2 once more..;)
I’ve noticed that sometimes blog can act a bit strange regarding new posts, I didn’t have any problems since I did this in site config. Here’s what I did...
Go to -> Tools -> Configuration , then scroll almost to the bottom and find, Published default, select Yes, and
Cacheable default, select No....
Maybe there was something I did later,but I dont remember
I’m also using DTD Xhtml 1.0 Strict, but really dunno if it matters anyway....
Hope this helps
Regards