xml - Android Bug? Multiple animations don't animate at the same time -

so i'm applying one animation multiple imageviews (arrows) , using animationset class so, see below:

animation animinstruct; //inside oncreate animinstruct = animationutils.loadanimation(this, r.anim.anim_instructions); imageview arrow_bottomright = (imageview) container.findviewbyid(r.id.arrow2); imageview arrow_bottomleft = (imageview) container.findviewbyid(r.id.arrow3); imageview arrow_topleft = (imageview) container.findviewbyid(r.id.arrow0); imageview arrow_topright = (imageview) container.findviewbyid(r.id.arrow1);  animationset start_atsame_time = new animationset(true); start_atsame_time.addanimation(animinstruct); arrow_topleft.setanimation(start_atsame_time); arrow_topright.setanimation(start_atsame_time); arrow_bottomleft.setanimation(start_atsame_time); arrow_bottomright.setanimation(start_atsame_time); start_atsame_time.start(); 

in xml (anim_instructions):

<alpha           android:fromalpha="0.0"     android:toalpha="1.0"      android:interpolator="@android:anim/accelerate_interpolator"      android:duration="1000"     android:repeatcount="5"  /> </set> 

however, when run application (on actual device), arrows fade in/fade out @ same time after first iteration, 1 arrow takes longer fade out while others stay on track each other. don't know if device's hardware limitations, android bug, or else?