This seems related. It's also possible I'm misunderstanding what is supposed to happen here.

If you create test.py with just the 2 lines:

"""
a

and run python test.py from CPython master, you get

$./python.exe test.py
  File "/Users/aaronmeurer/Documents/cpython/test.py", line 4
    a
    ^
SyntaxError: EOF while scanning triple-quoted string literal

Notice that it reports line 4 even though the file only has 2 lines.

The offset in the syntax error is 6 columns (line numbers and column offsets
in SyntaxErrors count from 1)

>>> try:
...     compile('"""\na', '<none>', 'exec')
... except SyntaxError as e:
...     print(repr(e))
...
SyntaxError('EOF while scanning triple-quoted string literal', ('<none>', 2, 6, '"""\na\n'))