This plugin is pretty good at what it does, but there are massive errors in the code which will break lots of peoples blogs.... but here is a fix...
In the "magazine-columns.php" file, in the "add_columns" function (at the top) the function uses echo at certain stages once it has processed some of the content.... this is what breaks peoples blogs!
The Fix:
Find if(stristr($content, '<!--column-->') && is_singular()) { at the start of the function (line 13 for me). Add a line after it that is something like $retval = "";.
Now go through the function and find any line that starts with echo (there should be four instances of this around lines 48, 62, 65, and 73). Change echo for $retval .=.
Go to the end of the function and just above the } else { add in return $retval;
This should make the function behave as WordPress intended e.g. edit the content then pass it back so that other functions can also make amends if required.
Summary:
These changes NEED to be added to a future release of this plugin, otherwise people will keep having confusing errors on their blogs.