Problem with completefunc and lists

I made a custom completefunc for email addresses from the tip here:
https://gitlab.com/muttmua/mutt/wikis/ConfigTricks

fun! CompleteEmails(findstart, base)
if a:findstart
let line = getline('.')
let start = col('.') - 1
while start > 0 && line[start - 1] =~ '[^:,]'
let start -= 1
endwhile
return start
else
let res = []
for m in split(system('completeemails ' . shellescape(a:base)), '\n')
call add(res, m)
endfor
return res
endif
endfun

fun! UserComplete(findstart, base)
let line = getline(line('.'))
if line =~ '^\(To\|Cc\|Bcc\|From\|Reply-To\):'
return CompleteEmails(a:findstart, a:base)
endif
endfun

And my completer script:

#################################
#!/bin/sh

afile="$HOME/.mutt/aliases"
base=$(echo "$@" | sed "s%^ %%g")

aliases=$(cut -d' ' -f2- $afile | grep -iE "^$base" | cut -d' ' -f2- \
| sed "s%^% %")
names=$(cut -d' ' -f3- $afile | grep -iE "^$base" \
| sed "s%^% %")
addresses=$(cut -d'<' -f2 $afile | cut -d'>' -f1 | grep -iE "^$base" \
| sed "s%^% %")

printf "%s\n%s\n%s" "$aliases" "$names" "$addresses" | sort -u
################################

When querying the script it works, but when I select an entry I get
": &" added to the end of the line.

This even happens if I put this in the top of the script:

echo " a"
echo " b"
echo " c"
exit

It doesn't do this when using a string, like the CompleteMonths()
example in the docs.

Why is it adding the ": &" to the end?

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