[fixed]Imperial Mask stops Null Caller +acts on stack

Describe the Bug:
1- I had Null Caller in play and creatures in my graveyard and AI cast Imperial Mask and then I couldn't activate Null Caller any more.When I destroyed Imperial Mask it became activate-able again.fixed
2- Imperial Mask gives hexproof to player while still being on stack.
Which card did behave improperly ?
Imperial Mask maybe also Null Caller for 1st bug?
Which update are you using?(date,name)Which type(Duel,Gauntlet,Sealed Deck)
Manalink 2016/08/27: Eldritch Moon v2, duel
What exactly should be the correct behavior/interaction ?
1- Null Caller doesn't target graveyard so it shouldn't be stopped by Imperial Mask (opponent's or your own) and moreover it only chooses card from your graveyard and so if an opponent has shroud shouldn't matter for any card that even targets you.
2- Imperial Mask doesn't give hexproof to player while still being on stack.
Are any other cards possibly affected by this bug ?
-
2- Imperial Mask gives hexproof to player while still being on stack.
Which card did behave improperly ?
Imperial Mask maybe also Null Caller for 1st bug?
Which update are you using?(date,name)Which type(Duel,Gauntlet,Sealed Deck)
Manalink 2016/08/27: Eldritch Moon v2, duel
What exactly should be the correct behavior/interaction ?
1- Null Caller doesn't target graveyard so it shouldn't be stopped by Imperial Mask (opponent's or your own) and moreover it only chooses card from your graveyard and so if an opponent has shroud shouldn't matter for any card that even targets you.
2- Imperial Mask doesn't give hexproof to player while still being on stack.
Are any other cards possibly affected by this bug ?
-