[MC-82681] Falling Sand Command Blocks Can't Use \(BackSlash)in ArmorStand's Holding Item NBT+ Tag

I summoned falling sand command block with command

/ summon FallingSand "/ execute [type =! Player, name = Unhak39] ~ ~ ~ / summon ArmorStand ~ ~ ~ {... \" extra \ "...}

.
But the commands of summoned command block is"

/ summon FallingSand "/ execute [type =! Player, name = Unhak39] ~ ~ ~ / summon ArmorStand ~ ~ ~ {... " extra  "...}

(BackSlash) is missing in the Command(NBT+ Tags of the Summon Entity's Holding Items)of the summoned command block