> I was confusing it with a regular exception, e.g.
> print("年",a)

I'm now invesigating this problem. This comes from another reason.
Please look at fp_setreadl in Parser/tokenizer.c.
This function opens file using codec and doesn't seek to current
position. (fp_setreadl is used when codecs is neigher utf-8 nor 
iso-8859-1 .... tok->decoding_state == STATE_NORMAL)

So

# coding: ascii
# 1
# 2
# 3
raise RuntimeError("a")
# 4
# 5
# 6

outputs 

C:\Documents and Settings\WhiteRabbit>py3k ascii.py

Traceback (most recent call last):
  File "ascii.py", line 6, in <module>
    # 4
RuntimeError: a
[22821 refs]

# One line shifted.

And

# dummy
# coding: ascii
# 1
# 2
# 3
raise RuntimeError("a")
# 4
# 5
# 6

outputs

C:\Documents and Settings\WhiteRabbit>py3k ascii.py

Traceback (most recent call last):
  File "ascii.py", line 8, in <module>
    # 5
RuntimeError: a
[22821 refs]

# Two lines shifted.