If “bash <file>” works, why is “source <file>” throwing an error?

I have the following script:

#!/bin/bash
set -x
if :; then
    echo a
fi

If I run bash /tmp/file, a is echoed, but if I run source /tmp/file, I get:

bash: /tmp/test: line 6: syntax error: unexpected end of file

The output:

knezi@holly tmp]$set -x; source /tmp/test; set +x
+ source /tmp/test
++ set -x
bash: /tmp/test: line 6: syntax error: unexpected end of file
+ set +x

knezi@holly tmp]$set -x; command source /tmp/test; set +x
+ set -x
+ command source /tmp/test
+ source /tmp/test
++ set -x
bash: /tmp/test: line 6: syntax error: unexpected end of file
+ set +x

knezi@holly tmp]$bash -c "source /tmp/test"
+ bash -c 'source /tmp/test'
++ :
++ echo a
a


knezi@holly tmp]$od -c /tmp/test
0000000   #   !   /   b   i   n   /   b   a   s   h  \n   s   e   t    
0000020   -   x  \n   i   f       :   ;       t   h   e   n  \n  \t   e
0000040   c   h   o       a  \n   f   i  \n
0000051

Output of commands shopt -p and set -o: http://pastebin.com/bsqc8aru

Output of set: http://pastebin.com/S9KpqZAL

declare -fp produces nothing.

I thought that source does the same as bash, but instead of starting new session rather runs the code in the current one. Can anyone explain this error to me?

I run bash GNU bash, version 4.2.53(1)-release (x86_64-redhat-linux-gnu).