Broken plot_background on gggrid

[IKupriyanov-HORIS]

Border around a plot is inconsistent.

Code snippet:

from lets_plot import *
LetsPlot.setup_html()

p = gggrid([
    ggplot() + geom_point() + coord_fixed(),
    gggrid([
        ggplot() + geom_point() + coord_fixed(),
        ggplot() + geom_point() + coord_fixed()
    ])
], ncol=1) + theme(plot_background=element_rect(size=3))

p

Result: