Usually you would have a small system that clears people who just died on a combat game. But for some reason, using the execute command on a dead person doesn't work while setting scoreboards, tp'ing and clearing do work.

What I expected to happen:
/execute on dead people would work normally like it does for /clear and /tp

What actually happened:
/execute'ing on a dead person results in the following error:
"The entity UUID provided is in an invalid format"

How to reproduce:

/scoreboard objectives add hasDied deathCount

create a redstone clock which powers commandblocks with the following commands.

/clear @a[score_hasDied_min=1]
/execute @a[score_hasDied_min=1] ~ ~ ~ say I died
/scoreboard players set @a[score_hasDied_min=1] hasDied 0