(the version of the game 1.5.0.7 and the device samsung galaxy j3 2016 (j320h) )to dedicate this bug i use this method :

I put two commamd block: 1. on repeat need redstone unconditional and the command /execute @e ~ ~ ~ /fill ~ ~-1 ~ ~ ~-1 ~ wool (and the ticking area was 70 *70 and the command blocks was in the middle)

2.on repeat need redstone unconditional and the command /kill @e 

*i make sure there is no mobs there

and i leave the area away ~2000 blocks far

I turn on spawn mobs and difficult was hard 

then using command i put redstone in front the command blocks 

the test period : ~5-10 min 

and the results is :

the area around player (which he was 2000 from ticking area) was full of dots of wool and it fourm aring 

i stop mobs spawning and put it on peacefull again

and remove the redstone from the command block ) and the area dosent have any wool block in the floor which mean no mobs had spawn their in the tickingarea