Function output cannot be redirected

[subnut]

$ hello() { HI=0xDEADBEEF; echo $HI; }
$ hello > /dev/null
0xDEADBEEF
$ exit

---

Expected output -

$ hello() { HI=0xDEADBEEF; echo $HI; }
$ hello > /dev/null
$ exit

[9ao9ai9ar]

This is really bad. I have a script running something like this:

while read -r word; do
    : work
done <<EOF
$(call_function)
EOF

and it just gets stuck at this part.