When I type the command:

/summon sheep 5 5 5

Then a sheep is summon facing South at location 5 5 5.

But when I put that same command into a function:

[baaaa.mcfunction]
summon sheep 5 5 5

And run it:

/function baaaa

Then the sheep is summoned copying my facing.

I'm not clear whether this is a bug or a feature however. I actually wouldn't mind using execute rotated 0 0 run summon sheep 5 5 5, as it would let me control facing for summons and save teleporting them after.