Yes, there was certain disturbing effect of the tiny and lonely Nanoarchaeum genome, yet the Halobacteria is a very specific clade, forming a tightly connected group and moving around as a whole, mainly due to the biased acidity of their constituent amino acids. We anticipate that the relative placement of Halobacteria with respect to other groups may stabilize when more genomes are used to construct a tree.
The placement of Halobacteria (due to interfering Nanoarchaeota, I presume) is also a little disturbing. I would recommend that the authors provide a discussion of this. Especially with regards to other archaeal trees. For instance, in the tree of Armanet et al 2011 that the authors also refer to, the placement of Halobacteria with respect to Nanoarchaeota is very different.