ppcbuyers - 8:50 pm on Aug 12, 2008 (gmt 0)

If you have broad match keywords, it could be that the system is determining what ad is relevant -- and the AdWords system doesn't limit its search to one Ad Group. If it finds that another ad IT deems "better", and it happens to be located within a different campaign and/or ad group in your account, then it could pull the ad located in the other campaign. This could be why the keyword level URL isn't working...ask your rep about it