Non square maps plot incorrectly using ggmap()

[lukeloken]

Reproducible Example

library(ggmap)
register_google(key = as.character(GoogleAPIkey))

#rectangle 
map_1<-get_googlemap(center=c(-121.57,38.51), size=c(250, 500), zoom = 12, scale=2, maptype = "satellite", key=GoogleAPIkey )

ggmap(map_1)

In the first example, the image appears twice and is compressed along the x-axis. It was downloaded using a rectangle size=c(250,500). Also notice that the longitude axis labels appear as they should.

#square 
map_2<-get_googlemap(center=c(-121.57,38.51), size=c(500, 500), zoom = 12, scale=2, maptype = "satellite", key=GoogleAPIkey )

ggmap(map_2)

In the second example, the image is downloaded as a square size=c(500,500). It plots correctly.