axisPhylo() not extending all along the root edge

[emmanuelparadis]

This was pointed out by @KlausVigo in #103 :

mytree2 <- read.tree(text = "((((((((((a:1,b:1))))))))));")
mytree2$edge.length <- runif(11)
mytree3 <- collapse.singles(mytree2, TRUE)

layout(matrix(1:2, 2))

plot(mytree2, root.edge = TRUE)
axisPhylo()
plot(mytree3, root.edge = TRUE)
axisPhylo()

In the second plot, the root edge extends far beyond the horizontal scale drawn by axisPhylo().