serious mysql latin1 to utf8 error, attention please

[ye tian]

I use php to insert a hex byte to a mysql table, and use select hex() to get the real data; set names latin1, and table 's charset is utf8, so there is a translation from latin1 to utf8.

Hex: \x88
select hex from mysql: CB86

but I usemb_convert_encoding($hex, 'utf8', 'latin1');
get result: c288

I use utf8 to encode by hand, and get the same result: c288.
so why mysql translate latin1 to utf8 not the same with the standard way????