Second axis doesn't appear when used with coord_map()

[Nekochef]

This issue appears when I'm trying to plot a map with axes on all the sides.
Here is an example:

if (require("maps"))
    states <- map_data("state")
    arrests <- USArrests
    names(arrests) <- tolower(names(arrests))
    arrests$region <- tolower(rownames(USArrests))

    choro <- merge(states, arrests, sort = FALSE, by = "region")
    choro <- choro[order(choro$order),]
    ggplot(choro, aes(long, lat)) +
    geom_polygon(aes(group = group, fill = assault)) +
    coord_map("rectangular", 38) +
    scale_y_continuous(sec.axis = dup_axis()) +
    scale_x_continuous(sec.axis = dup_axis())

And the map looks like:

As you can see, the second axes only appear with their names but not their labels and ticks.

It seems that this issue exists not only with coord_polar:> #2072.

And if I change coord_map() to coord_quickmap():

if (require("maps"))
    states <- map_data("state")
    arrests <- USArrests
    names(arrests) <- tolower(names(arrests))
    arrests$region <- tolower(rownames(USArrests))

    choro <- merge(states, arrests, sort = FALSE, by = "region")
    choro <- choro[order(choro$order),]
    ggplot(choro, aes(long, lat)) +
    geom_polygon(aes(group = group, fill = assault)) +
    coord_quickmap() +
    scale_y_continuous(sec.axis = dup_axis()) +
    scale_x_continuous(sec.axis = dup_axis())

The code works fine:

[hadley]

Unforunately, dual axes are currently only supported with Cartesian coordinate systems.