Different binary result returned by mysql function cast and preg_capture

[gitpypy]

Hi!
I met a problem when I was using preg_capture function to get some value.

First, I execute the following sql script:

select preg_capture('/([ⅠVIⅡⅢⅣ].{0,3}期)/', 'ⅣEA期' );

It returns the blob value �£EAæ��

And then, I execute the following sql script:
select cast('ⅣEA期' as binary) from dual;
It returns �EA�

I don't understand that why It missed an â when I execute the first sql script and that's not the right value I really want.

Help me please!
Thanks a lot.