Is this object an asteroid or comet, and how can it produce so many tails? The NASA Hubble Space Telescope Science Release HEIC 1320 - When is a Comet not a Comet? - Hubble astronomers observe bizarre six-tailed asteroid is self-explanatory, but it doesn't explain what actually happening.

Sometimes comets will show two tails, but one is usually identified with the path of the comet's orbit, and the other with the direction away from the sun. But this is an asteroid (or so it seems) and there are many tails with complex behavior.

edit: I've found this ArXiv preprint: The Extraordinary Multi-Tailed Main-Belt Comet P/2013 P5 where "main belt" refers to the main belt of asteroids, and yet the object is now called a comet.  Wikipedia lists both names and suggests both designations - asteroid or comet:


  311P/PANSTARRS also known as P/2013 P5 (PANSTARRS) is an asteroid (or main-belt comet) discovered by the Pan-STARRS telescope on 27 August 2013.(4) Observations made by the Hubble Space Telescope revealed that it had six comet-like tails.(5) The tails are suspected to be streams of material ejected by the asteroid as a result of a rubble pile asteroid spinning fast enough to remove material from it.(2)


It's been three point five years now - has this been figured out yet? Is it an asteroid or comet (or both), and how can it produce so many tails?


above: HST image of comet P/2013 P5 from here.


above: HST image (annotated) of comet P/2013 P5 from here.
A paper titled "Monte Carlo Models of the dust environment of a sample of comets from the Oort Cloud to the outer Main Asteroid Belt" (PDF also here) (2014) studied the behaviour of P/2013 P5 using models and concluded that


  
  The object has been subjected to an intermittent dust mass loss, most likely associated with a rotational disruption. This is confirmed
  from the analysis of both HST and GTC images. The total dust mass
  released was of the order of $10^7\ kg$, for particle density of
  $1000\ kg\ m^{−3}$ and geometric albedo $p_v = 0.04$.
  The model of rotational disruption, based on simulations of an object that loses mass from its equatorial region, and whose
  rotational axis is perpendicular to its orbit plane, reproduces to the
  last detail the observed complex brightness pattern at four different
  epochs of HST and GTC observations. For obliquities different from 0°
  or 180° , the fits get much worse. On the other hand, an isotropic
  ejection model does not fit the HST data because it produces much more
  diffuse tails than observed.
  The ejection velocities are very low, of the order of $0.02–0.05\ m s^{−1}$. This places the limit on the size of the object to be in the
  range $30–134\ m$ for assumed densities of $3000–1000\ kg m^{−3}$.
  


This seems to confirm what the original question cited as a possible explanation, i. e. 


  The tails are suspected to be streams of material ejected by the
  asteroid as a result of a rubble pile asteroid spinning fast enough to
  remove material from it.


The asteroid is loosely bound (a "rubble pile") and spinning fast, so everytime some of the boulders which form it shift a bit, some material may escape into space and form a small tail.