nrow(rbind(character(), character())) returns 2 (as documented but very unintuitive, IMHO)

In my experience, and more generally speaking, the desire to treat
0-length vectors as a special case that deviates from the
non-zero-length case has never been productive.

nrow(rbind(aa = c("a", "b", "c"), AA = character()))

[1] 1

By rights of the invariance that you and Hadley are advocating,  as far as
I understand it, the last should give 2 rows, one of which is all NAs,
rather than giving only one row as it currently does (and, I assume?,
always has).