NOTE: I have already searched with multiple search terms, and could not find anything similar to this. I'm surprised that it isn't reported regularly like some bugs are.

When summoning an entity that has some kind of modifier to make it invisible (potion effect, marker tag on armor stands, etc), it will briefly appear visible for one frame/tick (not quite sure which).

The bug can be seen in almost any case where invisible entities are spawned. Can be seen here: http://youtu.be/RNegSEY_QrU?t=2m49s

Possibly related to armor stands always spawning in the default rotation and then snapping to face the player.