some trouble with permalinks…

hello,

I changed almost all permalinks on my blog;Google actually finds both, the old url and the new one; obviously the old is redirected to the new one, correctly, BUT, this seems to result in a title and descritpion tag duplication issue according to Google webmaster’s tool reports.
Should I fix that issue?? Could I avoid that old urls are redirected to new ones?
Did someone come across such an issue??

Thanks