Background bleeds through in bottom right corner of (GTK) popup windows

[RicArch97]

Happens with about app pop ups, or file picker pop ups for example.

shadows_on_csd is disabled.

Sort of looks like as if the corner radius doesn't match there, while GTK uses 12 and corner_radius is also set to 12.

Screenshot:

[WillPower3309]

Is this still present? I'd like to hope this was fixed in scenefx