vterm prints extra spaces vs other terminals

[pedro-nonfree]

Enjoying living inside emacs and vterm everyday, today I found this:

the shell script test

echo 'bla1 bla2' > vtermtest-a
echo 'bla1 bla3' > vtermtest-b
echo 'bla2 bla3' > vtermtest-c
paste -s vtermtest-* | tr ' ' '\n' | sed '/^$/d' | sort -u
rm -f vtermtest-a vtermtest-b vtermtest-c

current behavior with vterm

[2025-10-16 Thu 20:25:18] $ echo 'bla1 bla2' > vtermtest-a
echo 'bla1 bla3' > vtermtest-b
echo 'bla2 bla3' > vtermtest-c
paste -s vtermtest-* | tr ' ' '\n' | sed '/^$/d' | sort -u
rm -f vtermtest-a vtermtest-b vtermtest-c




bla1
bla2
bla3
[2025-10-16 Thu 20:25:18] $ 

expected behavior (tested with xfce4-terminal)

[2025-10-16 Thu 20:24:38] $ echo 'bla1 bla2' > vtermtest-a
echo 'bla1 bla3' > vtermtest-b
echo 'bla2 bla3' > vtermtest-c
paste -s vtermtest-* | tr ' ' '\n' | sed '/^$/d' | sort -u
rm -f vtermtest-a vtermtest-b vtermtest-c
bla1
bla2
bla3
[2025-10-16 Thu 20:24:40] $ 

same happens with clean emacs 30.1 and latest stable vterm

Running latest stable release according to melpa vterm 20250929.1514

emacs -Q --eval "(progn
  (add-to-list 'load-path \"~/.emacs.d/elpa/vterm-20250929.1514/\")
  (require 'vterm)
  (vterm))"

output summary

extra spaces are added

current

bla1
bla2
bla3

expected

bla1
bla2
bla3