In line with the common doctrine among approved moralists, Fr. Royo Marín teaches in his Moral Theology for Laity  (Vol. I, No. 794):

"It is never lawful to lie ... But ... there are times when it is lawful to draw hand on the called mental restriction ...

We must distinguish between ambiguous terms, anfibología and mental restriction.

a) AMBIGUOUS TERMS are those having two or more meanings...

b) AMPHIBOLOGY is a phrase with a double meaning, one of which is not the common or usual ...

c) MENTAL RESTRICTION is a kind of anfibología, consists in moving with the mind an expression or phrase to a different meaning than it appears from the obvious meaning of the words ...

When can you say that there is just and proportionate reason to dip into this kind of mental restrictions?

Generally, the answer will be required always to hide the truth or when the neighbor makes one question recklessly that he has no right ...

It is not lawful, however, the use of  mental restriction when is a duty to expose the truth   faith, charity, justice, religion, and so on."

But Bishop Fellay's statement of 15/4/12 is "an ambiguous text, which in itself is a serious misconduct, because we can not want to rebuild the Church basing ourselves on a misunderstanding" (Brief reflection on the text of Doctrinal Preamble April 15, 2012, by a priest of the SSPX). Indeed, besides the outrageous claims unequivocal referred this article, the statement is full of mental restrictions, some of which are extremely dangerous (cf. "The Ambiguity of April", by Bishop Williamson).

Bishop Fellay must answer the following question: was he forced to hide the truth from modernist Rome or rather he was required to manifest the truth required by the faith, charity, justice and religion?

But,  Bishop Fellay would be able to answer without resorting to his usual mental restrictions? God grant us that mistake, but we do not think so, because that would force him to leave his attempt to reach a workable agreement with Rome, to apologize and resign, all necessary things, however, to remove the SSPX auto demolition process in which it is immersed.

A Priest of the SSPX
http://nonpossumus-vcr.blogspot.mx/2013/03/declaracion-doctrinal-de-mons-fellay-un.html