Images overlap plots in GridSpec

[droumis]

ALL software version info

panel v0.14.2

Description of expected behavior and the observed behavior

When plotting an image after a plot in a GridSpec, the image overlaps with the plot. I would have expected that the images would be stretched to fit into their assigned grid cells. Using sizing_mode='stretch_both' makes it worse.

Complete, minimal, self-contained example code that reproduces the issue

import panel as pn
from bokeh.plotting import figure

p1 = figure(width=300, height=300)
p1.line([1, 2, 3], [1, 2, 3])

gridspec = pn.GridSpec()

gridspec[1, 0:2] = p1

gridspec[0, 0:2] = 'https://upload.wikimedia.org/wikipedia/commons/4/47/PNG_transparency_demonstration_1.png'

gridspec

Using sizing_mode='stretch_both':

[philippjfr]

This is a known issue (although I can't find the earlier issue about this) and is related to the bokeh layout engine. This should be resolved automatically once we upgrade to Bokeh 3.0 with the new layout engine.