see attachment
Created attachment 93872 [details] error message from emerge
Previous revisions should fail as well, as there is no difference wrt patches; do you confirm it?
provide also emerge --info please.
Created attachment 93922 [details] emerge --info
Previous versions also fail. I had them masked out, but the revision bump brought r3 back into emerge -Du world cycle.
I'm closing this, as there haven't been any other complaints on this and I can't reproduce this anyway.