Overview

If you have a repeat command block on conditional mode and attach a trailing chain of chain command blocks to it, you can activate and deactivate all of the chain (including the repeat command block itself) by powering and unpowering the repeat command block with no problem, as long as it's condition is true, if however the condition is false, it strangely powers all the chain command blocks exactly once when receiving a redstone signal. If you keep it powered and instead change the state of the condition, then the execution of the repeat command block both starts and stops one tick earlier then the rest of the chain.

Exact reproduction steps

First you setup 4 command blocks:
(a) Impulse, Unconditional, Needs Redstone
(b) Repeat, Conditional, Needs Redstone
(c) Chain, Unconditional, Needs Redstone
(d) Chain, Unconditional, Needs Redstone

Here (a), (b), (c), (d) should be in a straight line with (a) pointing into (b), (b) pointing into (c) and (c) pointing into (d).

They have the following commands:

Then you try the following things

#1

Remove all redstone blocks from previous tests.
If you just did #3, you first need to create (a) again.
Do "/say ----------------", so you can later scroll through the chat and know where you started.

Power (a) with a redstone block.

Then Power (b) and quickly unpower (b) afterwards so you chat doesn't get spammed.

As you can see the redstone block activated and deactivated the repeat and chain command blocks as expected.

#2

Remove all redstone blocks from previous tests.
If you just did #1, you need to remove (a) and create it again so that it has SuccessCount data of 0.
If you just did #3, you might want to create (a) again, but it is actually not involved in this part of the bug reproduction.
Do "/say ----------------", so you can later scroll through the chat and know where you started.

Then power (b) with a redstone block.

As you can see, the repeat command block (b) doesn't execute any command, but upon being powered it powers the chain on it exactly once. I find this very strange and it seems buggy.

#3

Remove all redstone blocks from previous tests.
If you just did #1, you need to remove (a) and place it again so that it has SuccessCount data of 0.
You need to power (b) and keep it powered with a redstone block.
Do "/say ----------------", so you can later scroll through the chat and know where you started.

Then power (a) with a redstone block and quickly break (a) afterwards so you chat doesn't get spammed.

As you can see, (b) both starts and stops outputting one tick before (c) and (d) do.