"gradient" in geom_hilight does not work properly with coord_flip() or layout_dendrogram()

[PandengWang]

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Thanks so much for developing such a useful package!

The gradient.direction does not work properly when using dendrogram layout. Please see the following example:

tre <- rtree(5)
ggtree(tre) + 
  layout_dendrogram() +
  geom_tiplab(hjust = 0.5, align = T, vjust = 0)  +
  geom_hilight(
         mapping=aes(subset = node %in% 1:5,
                     node = node,
                     fill = label,
                     alpha = 1
                     ),
         type = "gradient",
         to.bottom = T,
         align = "both",
         show.legend = F
     )

or 

ggtree(tre) + 
  geom_tiplab(hjust = 0.5, align = T, vjust = 0)  +
  geom_hilight(
         mapping=aes(subset = node %in% 1:5,
                     node = node,
                     fill = label,
                     alpha = 1
                     ),
         type = "gradient",
         to.bottom = T,
         align = "both",
         show.legend = F
     ) + 
  coord_flip()

Is there a solution to this issue?

Thanks!