@yo' -- thanks. provided, of course, that "xyz" is identifiable. (which is why all ams bibliographies now require inclusion of the mr number in blbliographies. even to the point of using them, in many cases, as the "key" for cites when a manuscript must be rekeyed.)
@yo' -- glad to hear it. great care is expended on it, and it gets a thorough overhaul at least every decade.
@barbarabeeton also, it's helped me in proofreading; when a cited article got published while my article was processed, I simply wrote a comment: "[Fen12] is now MR123456"
@yo' -- because math reviews pays great attention to accuracy, ams now routinely replaces authors' bibliographies with amsrefs-formatted data. where it exists, of course. if someone is citing gauss or euler, no mr equivalent exists.
@Danu If this was a bug (as I also thought it was), it would concern tikz itself. But in fact what you described is exactly what tikz was designed to do. See sourceforge.net/p/pgf/bugs/240
The solution to your "problem" is to manually add the option anchor=south/north/east/west option to your labels (the default, of course, is anchor=auto)
(The "problem" happens when tikz automatically sets the anchor to be (in your example) southwest or southeast when you want it to be south.)
