Glass pane textures are mirrored on the rear despite glass panes not being 2D

Glass panes are two pixel thick blocks, so it'd be expected that the textures applied on the back faces were of constant orientation as the panes are not completely flat. This, however, is not the case.

This results in some ugly mirroring effects when crosses of glass panes are viewed from some angles, much like those demonstrated in MCPE-40646.