pr -COLUMN vs. wide characters

[Dan Jacobson]

Why doesn't the first line of this output line up?
$ cat f f|env - pr -2 -T
一二三 123                                  一二三 123
b２  00                             b２  00
Ｃ３                                Ｃ３
efg                                 efg

Same problem utf-8 or big5. It should line up on fixed width display
devices, some characters being twice as wide as others, regardless of
how many bytes are used to store them on disk, etc.