[Known/Fixed]Mirror Arena Shatter Damage

[Azeria 390]

 

A full health Golurk with Magnitude was used for this.

 

*    The following moves terminate this field effect, damaging all active Pokemon for 1/2 of their Max HP:
        Earthquake        Bulldoze            Boomburst        Hyper Voice            Magnitude

 

The ability No Guard is not stated to have any special interactions with the field:

 

 

The field does indeed break, but the shatter damage to both sides does not occur whatsoever.

[Marcello 436]

This appears to have just bene specific to Magnitude, and has been fixed for Public.