This was noted a few places on the internet last fall, but I just came across it. From the Fifth Circuit’s decision in Iracheta v. Holder:

In both Saldana’s case and other cases involving similar situations, DHS officers and the Administrative Appeals Office (“AAO”) within DHS have relied on provisions of the Mexican Constitution that either never existed or do not say what DHS claims they say. In Saldana’s case and in others, DHS has relied on the proposition that Article 314 of the Constitution of Mexico provides that children born out of wedlock may be legitimated solely by the subsequent marriage of their parents. See Matter of Reyes, 16 I. & N. Dec. 436 (BIA 1978) (citing Article 314 of the Constitution of Mexico for this proposition); In re: Applicant, 2008 WL 3990518, at *2 (AAO March 18, 2008) (relying on Article 314 and Reyes to deny a citizenship claim); In re: Applicant, 2007 WL 5360778, at *2 (AAO November 27, 2007) (same); In re: Applicant, 2007 WL 5337094, at *2 (AAO July 2, 2007) (same). At oral argument, however, the government conceded that Article 314 of the Constitution of Mexico does not exist and never did. [FN]
[FN:] It is unclear whether the government has previously acknowledged this error, which originated at the BIA in 1978, over three decades ago. See Reyes, 16 I. & N. Dec. at 436. However, DHS relied on Reyes as recently as January 2012 and relied explicitly on Article 314 as recently as 2008, in rejecting Saldana’s citizenship claims. Though the government attempted to dismiss this error as a mere “typo,” we cannot agree. It is unclear what legal authority the BIA actually relied on in Reyes. It may have been a provision of the applicable civil code, as opposed to the Constitution of Mexico. The substance of the law may or may not have been correct in Reyes, but the BIA’s mistake in citing a non-existent constitutional provision, perpetuated and uncorrected by DHS in subsequent years, prevented the agency from making the correct inquiries or possibly from applying the correct law in subsequent cases. That error has wound its way through multiple agency decisions in immigration matters, which are significant to the impacted individuals.

The original decision in Reyes is here. I found a translation of the Mexican constitution here, but now I guess I don’t know whether it’s accurate.