Blog post entry is not rendered properly when viewed in IE and Documentation Theme is activated. See screen shot:

Workaround

• Switch to another theme or
• Switch to another browser or
• In IE 'developer tools' (F12), select 'document mode: IE 7'

Tested out the same scenario in Confluence 4.x and 4.2.x however the problem no longer exist. Therefore, to completely eliminate the problem, upgrading your instance is the best option.