Many 404 errors since upgrade to 5

Since upgrading to v 5 I've been seeing many more 404's in Google WebMaster Tools.

I've traced it down to both Breadcrumbs and the "show Category" on posts.

Both of these seem to add an additional segment to the end of the url that's not in my structure. For example, when I go to the category blog for sewing & crafts from the menu (Url: /blogs/sewing-crafts) Breadcrumbs says /blogs/sewing-crafts/crafts

Thanks in advance for your help