Why there's no support value after re-rooting ?

[gouwei1]

Hi,

I followed the tutorial of Rooting phylogenetic trees (http://www.iqtree.org/doc/Rootstrap#inferring-unrooted-tree-with-outgroup) with the same data and code:
iqtree2 -s bovidae_outgroup.phy -p bovidae.nex -B 1000 -T AUTO -st NT2AA --prefix rev_aa_outg

While after re-rooting the tree on the outgroup (Wild_pig and Minke_whale), there is no support value between Yak and Cow. Why?
Also, I noticed that there's also no support value if there are more than 2 identical sequences. How to denote that in the phylogenetic tree display? How to distinguish the two kinds of blank in the figure annotation?

Yours,
Wei