I don't use website wizard. I use the regular text editor in file manager. Recently in the past couple of weeks Firefox upgraded to version 20.0. I've been doing a lot of copying and pasting and haven't experienced any problems as the kind you mention.
If you still have IE on your computer try testing it through that. Just one part of the page displaying a different size is not normal in the absense of obvious coding.
Sometimes there can be hidden formatting code in editors. You could try as a test copying the code to a text file .txt on your desktop, save it, then recopy it from that to your wizard and then see if the problems reoccur.
You are a long-time editor like me so you know that what you are experiencing is not normal. Bravenet makes tweaks sometimes in their system. If nobody else is reporting it (wizard users), then I guess a support ticket is in order. I'm currently experiencing jpg upload problems (separate post).