Saving to PDF via RStudio leaves drop shadow



I've noticed that when I save a plot via Export > Save to PDF in RStudio, it leaves a drop shadow at the bottom of the saved PDF. This does not occur when I save the same plot using ggexport() or ggsave(). The drop shadow is subtle; it shows up on screenshots on PDFs saved via Save to PDF when I c/p them into Word, for example, but when I take screenshots of plots saved using ggsave() or ggexport(), there is no drop shadow. Is there any way to remove the drop shadow?