Reproducing this bug with plain Emacs

1. Start emacs without any .emacs or .emacs.d/init.el files 

2. Start Inferior python mode by M-x run-python

3. Enter first line of multi-line statement, press Enter and then start entering second line

>>> for x in range(10):<RET>

...<TAB>pri

4. Now press C-M-i, it will complete it to `print`, then enter x so the second line looks like 

...     print x

5. Now press Enter

instead of a ... prompt you should get an error