Let’s examine the doctrine of Pope Pius IX in light of definitions of some of the words he has used in his declarations on the matter.
Revision (June 21, 2010):
In French, Italian, Portuguese and Spanish, the word translated into English as "sanction" is translated as "tolerated". It is quite possible that this is the word Leo XIII used. If so, then he did not actually teach heresy in Immortale Dei (since toleration does not equal approval, whereas sanction does). The Latin text will have the answer, but as it stands he still has no excuse for his words above in Arcanum, as well as those in Rerum Novarum, the heresies he professed before allegedly being "elected", etc..
What Must You Do To Get to Heaven?