thanks. deleting the web data file helped me out, but I agree that Opera should fix this and enable deleting Autofill data by using "Clear private data..."
On a Mac you can find your profile data path via Opera -> About Opera. in my case it was /Users/username/Library/Application Support/com.operasoftware.Opera
(current version 19.0.1326.63, Mac OS X 10.9.1)
HTH