This is hard to believe. According to Andrew C. McCarthy on NRO,
a website maintained by the Mexican secretary of foreign relations explains that U.S. agents, as a matter of routine, notify the Mexican government regarding the locations of civilian border-patrol groups.
Apparently aware that this is a powder keg, DHS is scrambling to justify itself. Initially, a CPB spokesman confirmed the assertions of the Mexican government website. Now, however, a back-peddling DHS is labeling the Daily Bulletin story “inaccurate.”
The DHS went from “of course we tell them, it’s no secret” to “no, we don’t tell them” to “well, we have to tell them.” The last of which is debunked at the above link.
Also see Michelle Malkin‘s page.