Thanks to John for pointing me in the right direction; the normalization charts were not helpful, but after spending some time with UAX#15 and looking at the actual Unicode database, I see what is going on here.
It seems strange to me that the Unicode book (where I initially looked) simply gives the decomposition for U+1F71 as U+03B1 followed by U+0301 with no indication that anything else is involved (and likewise for other characters with singleton decompositions, such as the angrstrom). If U+1F71 decomposes to U+03AC, why is the other decomposition still given? David
