DB<50> $a=" "

  DB<51> $b = $a+0      # $a will cache its numeric val

  DB<52> p !!$a         # still true
1
  DB<53> use Devel::Peek

  DB<54> Dump $a
SV = PVNV(0x3fbd6f8) at 0x4aeebe0
  REFCNT = 1
  FLAGS = (POK,pIOK,pNOK,pPOK)
  IV = 0                         # <-- integer
  NV = 0
  PV = 0x4c4fb58 " "\0           # <-- string
  CUR = 1
  LEN = 10

  DB<55> Dump $b
SV = NV(0x4aeedf0) at 0x4aeee08
  REFCNT = 1
  FLAGS = (NOK,pNOK)
  NV = 0

  DB<56>