There are two issues I've observed with the "execute" command, specifically with the /playsound and /spawnpoint commands.

To illustrate:

If I use this command:
execute @s[type=hs:dummy] ~ ~ ~ playsound mob.elf.haggle @a
the sound plays for everyone.
 
However, if I run this command:
execute @s[type=hs:dummy] ~ ~ ~ playsound mob.elf.haggle @a ~ ~ ~ 1 2
the sound only plays relative to the hs:dummy.
 
Same goes for this:
execute @s[type=hs:dummy] ~ ~ ~ spawnpoint @a 234 12 3456
works great, but,
execute @s[type=hs:dummy] ~ ~ ~ spawnpoint @a ~ ~ ~
makes the spawn point the same as the hs:dummy.
 
The expected result would be that the tildas after the playsound and spawnpoint command would be relative to whatever those commands are targeting, not what the "execute" was performed as.