.adv_irradmap_saveFileName method not working in maxscript

[GLASS-CANVAS]

When I call the ".adv_irradmap_saveFileName" method in a maxscript the listener indicates that it has successfully completed the command but when I look in the render scene dialogue the irradiance output remains empty and no vrmap file is saved once rendering is completed.
Strangely ".adv_irradmap_loadFileName" seems to work perfectly well.
The following script demonstrates the problem:

renderSceneDialog.close()
vr = renderers.current
vr.adv_irradmap_mode = 1
vr.adv_irradmap_loadFileName = "filename.vrmap"
vr.adv_irradmap_saveFileName = "filename.vrmap"

Is this a bug, or am I overlooking something?