Sourcing a bash script and assigning a value to variable via backtick execution

Question

I have a strange problem with bash that I cannot explain.

I created the script test.sh which contains the lines:

export TEST_HOME=`ls -d $HOME`
echo $TEST_HOME
if [ "$HOME" = "$TEST_HOME" ]
then
  echo "Equal"
else
  echo "Not equal"
fi

Now if I source test.sh:

$ . test.sh

the output is

/home/sven
Not equal

However, if I make it executable and run it as a normal script:

$ test.sh

the output is

/home/sven
Equal

Any explanation how this behavior is explained? I am using RedHat 5.

Best regards,

Sven