Why doesn't chart_Series look right?

library(quantmod)
getSymbols("SPY", src = "yahoo")
## [1] "SPY"

This looks fine

chartSeries(SPY)

plot of chunk unnamed-chunk-2

But, why does this look wrong? i.e. instead of being aligned at the left margin, there is a box with a question mark.

chart_Series(SPY)

plot of chunk unnamed-chunk-3 plot of chunk unnamed-chunk-3