The bug
If you left click on the Ender Dragon to spectate through its eyes, nothing happens. If you press shift after this happens, you are telported to the current position of the dragon, as if you had been spectating. Between the time that you click on the dragon and the time that you press shift, you can move around freely.
By contrast, spectating the dragon using /spectate @n[type=ender_dragon] does work somewhat– the command makes you spectate the main dragon hitbox, rather than the head as would be expected.
Linked issues
is duplicated by 13
MC-280289
Spectating Ender Dragon doesn't function normally.
Resolved
MC-271616
I can not possess the ender dragon in the spectator mode
Resolved
MC-266410
Spectating the Ender Dragon doesn't work
Resolved
MC-258393
Problems spectating Ender Dragon [More Detail --> + New unmentioned Problems]
Resolved
MC-47826
Spectator mode-Bug
Resolved
8 more links
Comments 24
14 more comments
Happens to me too, exactly as you describe.