Yea i checked that and experienced the same problem, for every call a whitespace is added,
You can trim all the existing out by using
{.set account|$1|notes={.decodeuri|{.replace|%0A%0D||{.encodeuri|{.trim|{.get account|$1|notes.}.}.}.}.}.}
and to avoid it u have to set the entire notes again, but trimmed
ieither by adding a line after every call or adding an alias and using it instead , like :
[special:alias|private]
addnote={.set account|$1|notes key=$2=$3.}{.set account|$1|notes={.trim|{.get account|$1|notes.}.}.}