Problems with git-subtree pull with merging - git-subtree

Question

The following bash script code creates an example of using git-subtree. Please answer why the last command ends up causing a conflict "both added" while merging.
#! /usr/bin/env bash
declare TEST_ROOT=/tmp
declare TEST_DIR='test-subtree' ;
cd $TEST_ROOT && \
find $TEST_DIR -name "*" -maxdepth 1 -exec rm -rvf '{}' \; -prune
rm -rf $TEST_DIR ;
declare REPOS_ROOTS=$TEST_ROOT/$TEST_DIR/roots ;
declare REPOS_WORKDIRS=$TEST_ROOT/$TEST_DIR/workdirs ;
declare MAIN_REPO_NM='main_repo' ;
declare SUB_REPO_NM='sub_repo' ;
declare MCWD= ;
[ -d $TEST_ROOT/$TEST_DIR ] || \
mkdir -vp $TEST_ROOT/$TEST_DIR && cd $TEST_ROOT/$TEST_DIR && {
[ -d $TEST_DIR/${MAIN_REPO_NM}.git ] || git init --bare --shared ${MAIN_REPO_NM}.git ;
[ -d $TEST_DIR/${SUB_REPO_NM}.git ] || git init --bare --shared ${SUB_REPO_NM}.git ;
[ -d roots ] || mkdir -v roots ;
[ -d workdirs ] || mkdir -v workdirs ;
git clone --shared --separate-git-dir=$REPOS_ROOTS/$MAIN_REPO_NM ${MAIN_REPO_NM}.git workdirs/$MAIN_REPO_NM ;
git clone --shared --separate-git-dir=$REPOS_ROOTS/C1-$MAIN_REPO_NM ${MAIN_REPO_NM}.git workdirs/C1-$MAIN_REPO_NM ;
git clone --shared --separate-git-dir=$REPOS_ROOTS/$SUB_REPO_NM ${SUB_REPO_NM}.git workdirs/$SUB_REPO_NM ;
MCWD=$(pwd);
cd workdirs/$SUB_REPO_NM && {
cat > testfile.txt <<EOF
some lines of text
EOF
touch .gitignore ;
git add . ;
git commit -am 'add: new file initial commit' ;
git push origin master ;
git checkout master -b mainwork ;
git push --all ;
cd $MCWD ;
}
MCWD=$(pwd);
cd workdirs/$MAIN_REPO_NM && {
touch .gitignore ;
git add . ;
git commit -am 'initial commit' ;
git push origin master ;
git checkout master -b mainwork ;
git checkout -b mainwork-$SUB_REPO_NM ;
git remote add -f remote-${SUB_REPO_NM} $TEST_ROOT/$TEST_DIR/${SUB_REPO_NM}.git ;
git subtree add --prefix ${SUB_REPO_NM}.dir remote-${SUB_REPO_NM} mainwork --squash ;
git push --all ;
}
cd $MCWD ;
MCWD=$(pwd);
cd workdirs/C1-$MAIN_REPO_NM && {
git fetch --all ;
git remote add -f remote-${SUB_REPO_NM} $TEST_ROOT/$TEST_DIR/${SUB_REPO_NM}.git ;
git checkout mainwork-$SUB_REPO_NM ;
git pull --no-rebase --strategy=recursive -X theirs orign ;
cat >> ${SUB_REPO_NM}.dir/testfile.txt <<EOF
some lines of text was chnged
EOF
cat > ${SUB_REPO_NM}.dir/testfile-1.txt <<EOF
some lines of text was added
EOF
git add . ;
git commit -am 'some changes to, subtree: '"${SUB_REPO_NM}.dir" ;
git subtree push --prefix=${SUB_REPO_NM}.dir remote-${SUB_REPO_NM} mainwork-feature ;
cd ../$SUB_REPO_NM && {
printf -- 'Try to pull from: `%s\''\n' "origin mainwork-feature" ;
git checkout mainwork ;
git pull --no-rebase --strategy=recursive -Xtheirs origin mainwork-feature ;
git checkout - ;
git push origin mainwork ;
cd - ;
}
}
cd $MCWD ;
MCWD=$(pwd);
cd workdirs/$MAIN_REPO_NM && {
git fetch remote-${SUB_REPO_NM} mainwork ;
git fetch --all ;
git checkout mainwork-$SUB_REPO_NM ;
git pull --no-rebase --strategy=recursive -X theris origin mainwork-$SUB_REPO_NM ;
git subtree pull --prefix ${SUB_REPO_NM}.dir remote-${SUB_REPO_NM} mainwork --squash ;
cat >> ${SUB_REPO_NM}.dir/testfile-1.txt <<EOF
some lines of text was changed ;
EOF
git commit -am 'changes in: '${SUB_REPO_NM}.dir/testfile-1.txt ;
git subtree push --prefix=${SUB_REPO_NM}.dir remote-${SUB_REPO_NM} mainwork-feature ;
cd ../$SUB_REPO_NM && {
git checkout mainwork ;
git pull --no-rebase --strategy=recursive -Xtheirs origin mainwork-feature ;
git checkout - ;
git push origin mainwork ;
cd - ;
}
git fetch remote-${SUB_REPO_NM} mainwork ;
git subtree pull --prefix ${SUB_REPO_NM}.dir remote-${SUB_REPO_NM} mainwork --squash ;
}
cd $MCWD ;
MCWD=$(pwd);
cd workdirs/C1-$MAIN_REPO_NM && {
git fetch remote-${SUB_REPO_NM} mainwork ;
git checkout mainwork-$SUB_REPO_NM ;
git subtree pull --prefix ${SUB_REPO_NM}.dir remote-${SUB_REPO_NM} mainwork --squash ;
}
}
I used a similar syntax and everything worked fine, at least there was no merge problem. Unfortunately, there is no previous example that works.