I often see HTML pasted in from Microsoft Word. It has a lot of non-standard and irrelevant code in it, so sometimes it breaks our systems. It’s also hard to edit afterwards.
An easy way to clean that up is to paste it into Windows Live Writer using Edit > Paste Special > Thinned HTML, which removes most of the Microsoft Word extras while leaving the basic formatting in place. You can then copy-and-paste it into the blog/wiki editor. You can also use View > Source to get the HTML source code, which you can paste into the HTML mode of the blog/wiki editor.
Hope that helps!