I set up a command block system with the new repeat and chain command blocks. I have an armor stand with the tag "FightRobot", without any special attributes, and a command block that is constantly running (20 times / sec), which is executing every entity with the tag "FightRobot" to execute all players within 4 blocks to summon A ThrownPotion 5 blocks above their position. That all works fine. If I'm in gamemode survival and get killed by the potions (they are harming potions, by the way), the armor stand turns invisible, although when I check it with the entitydata command, it says "Invisible:0b". It still executes the commands to all players (summons the potions), and when I relog, it is visible again.

This is the command I used to summon the armor stand:
summon ArmorStand ~2 ~ ~

{Tags:["FightRobot"]}

This is the command that is constantly run:
execute @e[tag=FightRobot] ~ ~ ~ execute @r[type=Player,c=1,rm=1,r=4] ~ ~ ~ summon ThrownPotion ~ ~5 ~ {Tags:["damagerpotion"],Potion:{id:potion,Damage:8204,tag:{CustomPotionEffects:[

{Id:7,Amplifier:0,Duration:20,ShowParticles:0b}

]}},CustomName:FightBot}

The minecraft crash report after manually crashing the game:

---- Minecraft Crash Report ----
// Would you like a cupcake?

Time: 13.09.15 12:09
Description: Manually triggered debug crash

java.lang.Throwable
at azx.s(SourceFile:1625)
at azx.as(SourceFile:928)
at azx.a(SourceFile:377)
at net.minecraft.client.main.Main.main(SourceFile:125)

A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

– Head –
Stacktrace:
at bid.a(SourceFile:366)

– Affected level –
Details:
Level name: MpServer
All players: 1 total; [bkc['ColoredCarrot'/1350296, l='MpServer', x=-523,46, y=56,00, z=682,85]]
Chunk stats: MultiplayerChunkCache: 1087, 1087
Level seed: 0
Level generator: ID 01 - flat, ver 0. Features enabled: false
Level generator options:
Level spawn location: World: (-521,56,693), Chunk: (at 7,3,5 in -33,43; contains blocks -528,0,688 to -513,255,703), Region: (-2,1; contains chunks -64,32 to -33,63, blocks -1024,0,512 to -513,255,1023)
Level time: 27011 game time, 6000 day time
Level dimension: 0
Level storage version: 0x00000 - Unknown?
Level weather: Rain time: 0 (now: false), thunder time: 0 (now: false)
Level game mode: Game mode: creative (ID 1). Hardcore: false. Cheats: false
Forced entities: 2 total; [wv['Armor Stand'/1350295, l='MpServer', x=-518,50, y=56,00, z=687,50], bkc['ColoredCarrot'/1350296, l='MpServer', x=-523,46, y=56,00, z=682,85]]
Retry entities: 0 total; []
Server brand: vanilla
Server type: Integrated singleplayer server
Stacktrace:
at bid.a(SourceFile:366)
at azx.b(SourceFile:2369)
at azx.a(SourceFile:386)
at net.minecraft.client.main.Main.main(SourceFile:125)

– System Details –
Details:
Minecraft Version: 15w37a
Operating System: Windows 7 (amd64) version 6.1
Java Version: 1.8.0_25, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 597527416 bytes (569 MB) / 890966016 bytes (849 MB) up to 1060372480 bytes (1011 MB)
JVM Flags: 6 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx1G -XX:+UseConcMarkSweepGC -XX:+CMSIncrementalMode -XX:-UseAdaptiveSizePolicy -Xmn128M
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
Launched Version: 15w37a
LWJGL: 2.9.4
OpenGL: GeForce GTX 980/PCIe/SSE2 GL version 4.5.0 NVIDIA 355.82, NVIDIA Corporation
GL Caps: Using GL 1.3 multitexturing.
Using GL 1.3 texture combiners.
Using framebuffer objects because OpenGL 3.0 is supported and separate blending is supported.
Shaders are available because OpenGL 2.1 is supported.
VBOs are available because OpenGL 1.5 is supported.

Using VBOs: No
Is Modded: Probably not. Jar signature remains and client brand is untouched.
Type: Client (map_client.txt)
Resource Packs:
Current Language: English (US)
Profiler Position: N/A (disabled)
CPU: 8x Intel(R) Core(TM) i7-4790K CPU @ 4.00GHz