Mobs not properly oriented when rotated inside boats

When summoning a mob as a passenger inside a boat,

/summon minecraft:boat ~ ~1 ~ {Passengers:[{id:armor_stand}]}

and rotating the passenger any degree along the y-axis using a teleport command,

/execute as @e[type=minecraft:armor_stand] at @s run tp @s ~ ~ ~ ~180 ~

the mob's orientation is nowhere close, and sometimes even looks a different direction on a completely separate axis. The disorientation is not consistent, either, as sometimes teleporting the same amount along the same axis will have varying degrees of misalignment.