ARC/newruntime memory corruption

[zedeus]

I don't know why it happens and slightly changing the input can fix it. It also happens with #12823

import strutils, sequtils, strmisc, sugar

let input = @["KXSC, BGMC => 7 PTHL", "PXFX => LBZJ", "WXRQ, ZSCZD => HLQM"]

type
  Reaction = object
    output: string
    input: seq[string]

let reactions = collect(newSeq):
  for l in input:
    let (i, _, o) = l.partition(" => ")
    Reaction(output: o, input: @(i.split(", ")))

echo reactions
echo reactions

Output:

@[(output: "7 PTHL", input: @["KXSC", "BGMC"]), (output: "LBZJ", input: @["PXFX"]), (output: "HLQM", input: \x00\x00\x00", "\x00\x00\x00\x00"])]
@[(output: "(outpu", input: @["KXSC", "@[\"K"]), (output: "LBZJ", input: @["P[\"P"]), (output: "HLQM", input: \x00\x00\x00", "\x00\x00\x00\x00"])]

Changing the code slightly will trigger a segfault:

@[(output: ("PTHL", 7), input: @[("KXSC", 1), ("BGMC", 1)]), (output: ("LBZJ", 1), input: @[("PXFX", 1)]), (output: ("HLQM", 2), input: @[("WXRQ", 2), ("\x00\x00\x00\x00\x00", 12)])]
Traceback (most recent call last)
/home/zed/.choosenim/toolchains/nim-#devel/lib/system.nim(984) bug
/home/zed/.choosenim/toolchains/nim-#devel/lib/system/alloc.nim(945) dealloc
/home/zed/.choosenim/toolchains/nim-#devel/lib/system/alloc.nim(860) rawDealloc
/home/zed/.choosenim/toolchains/nim-#devel/lib/system/avltree.nim(74) del
SIGSEGV: Illegal storage access. (Attempt to read from nil?)