1.> Reusable content is added to an html field control as shown below

2.> Under the "Reusable Content" inserted into the page inside the same field contrl, add any OOTB web part.
3.> When you save or publish the page, the html gets mixed around and displays incorectly.
Hypothesis: I have to think this is a bug as each item can be added individually.
Possible Resolution:
- Use different page layouts with more field controls or
- programatically retrieve the reusable content and display it or
- Use a dataview WP with custom xslt to display the reusable content.
Tip: Reusable content is similar to what it was in MOSS, it is available if the SharePoint Server Publishing feature is activated in both the "Site Collection Features" & "Manage Site Features".
Additional info: Serge Luca confirmed this issue.