MC-1058 fixed indeed the issue that most entities cannot be seen when on the edge of the screen, but from my testing it seems that only applies to mobs/living entities and normal-sized blocks on ArmorStands.
On an ArmorStand with a large model on headslot though this rendering bug still occurs, both at edge of screen as well as frontal (when you look upwards), depending on block model.
Summon command for dragon head on ArmorStand headslot:
/summon minecraft:armor_stand ~ ~ ~ {ArmorItems:[{},{},{},{id:stone,Count:1}]}
It also affects self-made models, see screenshots and attached test-resourcepack by @unknown
This bug is important for mapmakers to be fixed before 1.9 release.
Two other things important to mention:
*Do not test on Y = 63* if you want to confirm it.
There is a (confirmed it by testing) bug that renders any entity (or the blocks attached to them) invisible if you're at Y= 63.
I'm not sure if this bug here can relate to it, but I'll leave the according bugpost in here to be safe, maybe you can fix it alongside this bug here:
MC-88176
*Do not test with ArmorStands that have their Marker-tag set to true*
I don't know whether or not it's "works as intended", but even regular-sized blocks vanish at certain perspective angles (sideways as well as looking up) if they're at an ArmorStand with Marker-tag set to 1. (Screenshots attached).
*It would be nice to know if this is intended behaviour* or - at least currently - not fixable, because I could think about some circumstances where it'd be nice to have an ArmorStand with Marker-tag set to true, but without the model/block "vanishing" out of sight of the player, dependant on their perspective.
*If this is maybe even a desired behaviour is up to Mojang and suggestions of the mapmaking community* - So i hope someone could comment on that.
If this is not intended behaviour and fixable, please fix it alongside with this bug.
@unknown opened a bugpost for this here on MC-98146
I suspect this might happen with any larger-scaled model, also selfmade models, I couldn't confirm that yet but will do so with according screenshots.If any modelmakers read this and could test it themself with a largescale model on an ArmorStand headslot to confirm it via a comment and screenshot, I'd be very thankful }=)
Thank you.
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I just tested it with a really quick made resource pack (I basically made the largest stone block ever) and can confirm it. It is also the case for item drops.
Screenshots + resource pack attached. (do
/summon minecraft:armor_stand ~ ~ ~ {ArmorItems:[{},{},{},{id:stone,Count:1}]}
On the left side of my screenshots the stone is the head of an ArmorStand, on the right side it is an item drop.

@unknown Thank you so much! 💙
Then it's even more important that it gets fixed before 1.9 release as it's very important for mapmakers!
Danke 😸

Can confirm. I tested with a giant model being held by a giant, which did disappear when looking upwards. Also happened with the model on an armor stand.
Confirmed for 16w07a

Really sad this isn't fixed yet. Ruins so much things 😞
Can confirm for 16w32a
Also I changed the command of my comment, so it works properly in the current 1.11-Snapshot. Entity names changed.
It stops rendering when the entity stops rendering.

@unknown I don't know how I shall interpret that.. That's exactly the thing, it'd be great if the entity wouldn't stop rendering as long as a bit of it is within the field of view of the player, and that's what is happening here, the entity, e.g. an ArmorStand (without true Marker) with equipment does not render that equipment although it's still within the screen/field of view of the player.
It has gotten way better than in the beginning at the very least, so if it can't be fixed any better than what we've got currently, then we'll have to live somehow with it.
Edit: I didn't have the time yet to test it in 16w32a myself, will do some tests after work; if the entity gets rendered whereas its equipment doesn't, I'll post it to Mojira-Reddit with the hope maybe something can be still done about it, if one sees some examples.
Just a quick feedback note from other map and concept makers:
They see it as important that a large model (or any equipment) can be displayed despite the entity not being rendered, if it's possible code-wise, for better immersion of the player.
One thing I find very important (which I also mentioned in the bugpost):
I hope it's possible to make Marker:1b-Armorstands render their equipment at any time, because that'd be very much important for mapmakers, as it breaks immersion of players in maps greatly when it stops rendering its equipment: MC-98146
Thank you }=)
PS: Opened a Redditpost for further discussions about that topic, without knowing of course currently if having equipment on an entity being visible despite that entity not being rendered.

@unknown The issue is that the rendering does not account for models that exceed their natural size.
If an entity is holding a block that is visually 3x wider than the entity itself, it makes little sense for that entity to stop rendering before the large block model is also out of a player's field of view.