My system is good in 17w17b look picture 6 and 7.
and in 17w18a and 17w18b is full bug.

Look my system in picture 1,2,3,4.
Ok so now look my picture 5.
my system is not powered but he placed a block of redstone and placed air block.

Steps to reproduce:

1. create a scoreboard
/scoreboard objective create Mana dummy Mana
/scoreboard objective create Timer dummy Timer
Next to create a new system with 4 command block
Command block repeat /scoreboard player add Time Timer 1
Command block chain /scoreboard player test Time Timer 200
command block chain conditional /scoreboard player add RedTeam Mana 5
command block chain conditional /scoreboard player remove Time Timer 200

2. place 4 command block (2 command block chain always active conditional) and (2 block of redstone repeat need redstone inconditionel)

The first system
in repeat /scoreboard player test RedTeam Mana 50
in chain /setblock ~ ~2 ~ minecraft:redstone_block
next to the first system. create a seconde system.
in repeat /scoreboard player test RedTeam Mana -10000 49
in chain /setblock ~1 ~2 ~ minecraft:air

3.with one command fill a redstone block for activate they 2 system and look the bug.
/fill ~ ~ ~ ~ ~ ~ minecraft:restone_block

Sorry for my english i speak bad english,im french.