This appears to occur currently on ArmorItems/HandItems (all entities) and Rotation (armor stand) under certain circumstances.

When a NoGravity armor stand is summoned, and then a tp or entitydata cmd is run to alter its rotation in the same tick after the summon, the rotation of the entity does not visually update, however the rotation tag in the entity does update.

When an armor stand any entity is summoned with hand or armor items, and then updated in the same tick to have air in the slot, the item will remain visually from the summon, but the tag in the entity has no item set.

Does not occur with Pose tag.

*To test (Rotation issue):*

1. impulse:

/summon ArmorStand ~ ~1 ~ {NoGravity:1b}

– Then run this into the following two cmds to test both entitydata and teleport

2a. chain (running from the impulse cmd):

 /entitydata @e[type=ArmorStand,r=4] {Rotation:[90.0f,0.0f]}

2b. chain (running from the chain cmd):

 /tp @e[type=ArmorStand,r=4] ~ ~ ~90 ~

3. Power the chains and run the impulse cmd. Notice visually, the armor stand is not facing the right direction, however if one looks inside its nbt by /entitydata, its rotation value will have been updated.

4. Try updating the armor stand again using the same cmds used in 2a as well as trying

 /tp @e[type=ArmorStand,r=4] ~ ~ ~ ~

to see that rotation still does not visually update. It only updates once you apply a different value and then switch it back after.

5. Try this again using NoGravity:0b to see that the rotation DOES visually update, likely because the armor stand is moving and so rotation is being updated.

*To test (Armor/Hand items issue):*

1. impulse:

/summon ArmorStand ~ ~1 ~ {ArmorItems:[{},{},{},{id:stone}],HandItems:[{id:stone}]}

– Then run this into the following two cmds to test both entitydata and replaceitem to replace the item with air (this only occurs with removing the item)

2a. chain (running from the impulse cmd):

 /entitydata @e[type=ArmorStand,r=4] {ArmorItems:[],HandItems:[]}

2b. chain (running from the chain cmd):

 /replaceitem entity @e[type=ArmorStand,r=4] slot.armor.head air

3. Power the chains and run the impulse cmd. Notice visually, the armor stand still retains the items, however if one looks inside its nbt by /entitydata, its armor/hand items will have been updated to have no item.

4. Try updating the armor stand again using the same cmds used in 2a and 2b to see that equipment still does not visually update. It only updates once you apply different items and then switch it back after.

5. Try this again using an item instead of air in 2a/2b to see that the item updates this time, possibly due to different treatment of removing items vs replacing with another item.