julia savefig() saves wrong marker shape

Question

The code is to using PyPlot to scatter and save in julia.

using PyPlot;pygui(true)

fig = figure()
for i = 1:400

    scatter([i,i+1], [i+1, i+2], color = "blue", s = 0.1)
end
PyPlot.savefig("1.png", figsize = (16, 9),dpi = 1200, bbox_inches="tight")

But the plot result and saved figure is different: What I want is some simple dots:

But in saved figure the marker shape is circles :

As you can see, the marker type is changed. I found this only occurs when scattering highly dense dots. How should I fix this?