Collapsing clade in circular layout gives curved min/max/mixed triangles

[AroneyS]

When clades are collapsed in circular layout, the "triangle" representation is curved.

nwk <- system.file("extdata", "sample.nwk", package = "treeio")
tree <- read.tree(nwk)
p1 <- ggtree(tree) %>%
  collapse(node = 21, "mixed")

p2 <- ggtree(tree, layout = "circular") %>%
  collapse(node = 21, "min")

p3 <- ggtree(tree, layout = "circular") %>%
  collapse(node = 21, "max")

p4 <- ggtree(tree, layout = "circular") %>%
  collapse(node = 21, "mixed")

e.g. p4