Plots (PyPlot) - Set legend title font size

Hi,
When using Plots (PyPlot backend) I cant seem to control the font size of the legends title:

using Plots, LaTeXStrings
pyplot()

upscale = 2 #Xx upscaling in resolution
p=plot( )
fntsm = Plots.font("sans-serif", pointsize=round(10.0*upscale))
fntlg = Plots.font("sans-serif", pointsize=round(14.0*upscale))

plot!(legendtitle="this legend title font is too small")
default(titlefont=fntlg, guidefont=fntlg, tickfont=fntsm, legendfont=fntsm)
default(size=(600*upscale,400*upscale))


scatter!(Plots.fakedata(50, 5))


plot!(title=("Graph title"))
plot!(xlabel =latexstring("\$x\$ label"))
plot!(ylabel =latexstring("\$y\$ label"))

Any ideas?

Cheers,
Tim