If an armadillo is in a rolled state, and begins to unroll but something that would cause it to roll up once more occurs during this animation, it can immediately turn back into its rolled form, which can look strange (head instantaneously disappearing rather than receding inward naturally). See attached video.
Thanks for Reporting this to MoJira!
But i have to disapoint you… This isnt a Bug.
The Armadillo just gets scared when you go near it so it gets back in the Rolled state!
-Toucka