Like this:
It should look like this:
It is only doing this on a seemingly random basis. Most pages work fine. There are no images posted in the threads that are affected, so it's not images blowing the size out. I'm not sure which tpl file controls this. I tried editing the size in the modify_body file, changing the table width from 100% to a fixed size, but that had no affect.
Any help will be greatly appreciated