ggplot2 polygon world map centred with limits gives funny edges

Using the below code I generate a map centred on Washington DC. solution based on kohske's solution here. I have changed `geom_path` to `geom_polygon` as I want to colour the countries. All is well and good until I want add the `scale_x_continuous` (commented so you can see that there's no problem when it is left out), this makes Antarctica and China look very strange, i guess because the polygons have been trimmed? Is there a known workaround for this? Help is appreciated. ``` library(maps) library(maptools) library(ggplot2) home_country_longitude <- -77.03 mp1 <- fortify(map(fill=TRUE, plot=FALSE)) mp2 <- mp1 mp2$long <- mp2$long + 360 mp2$group <- mp2$group + max(mp2$group) + 1 mp <- rbind(mp1, mp2) if(home_country_longitude < 0){ mp$long <- mp$long - (360 + home_country_longitude) } else { mp$long <- mp$long + home_country_longitude } ggplot() + geom_polygon(aes(x = long, y = lat, group = group), data = mp) + #scale_x_continuous(limits = c(-180, 180)) + theme(panel.background = element_rect(fill = "#090D2A"), panel.grid.major = element_blank(), panel.grid.minor = element_blank()) ```