Mobs are invisible through stained glass pane in hand of other mobs

You can't see mobs if you watch through glass pane that is held by other mob. To see it just summon some zombies with egg, and then summon giant with white glasspane:

/summon Giant ~ ~ ~ {HandItems:[0:{id:"minecraft:stained_glass_pane",Count:1b,Damage:1s}]}

Notice that some of the zombies are seen through glass in attached screenshot

bug searched by tags: through glass pane