As we can see, projective buffer transitions achieve better precision than standard transitions, but this is not surprising since they act only on "easy" arcs of length 1.
as can be seen in the table, even though the pseudo-projective parser is able to capture nonprojective syntactic phenomena, the algorithm with projective buffer transitions (which is strictly projective) outperforms it in four of the eight treebanks, including non-projective treebanks such as the German one.