Why would registering for the electoral Role Negatively effect your credit rating?

Right, so I signed up to Experian to check my credit rating, it was not the best and it suggested to improve my credit Rating I ensure I was on the Electoral Role for my current address. Turns out I wasn't, so I registered, now says I am on it in my credit report and my credit Rating has dropped 100 points. What? Why? Total opposite of what it should do right?