Strange subject charset

i am using rt 3.4.5 now and tried to upgrade to 3.8.0 in another machine.
after upgrade, i found the Chinese characters in the subject of old
tickets become “???”.
others fields are ok.

i go to the attachment table with phpMyAdmin and found situation below:

the subject data in rt 3.4.5 table is encoded by some method. it’s not utf8.
but the subject data present as utf8 correctly in browser.

after upgrade:
the subject data in rt 3.8.0 table is now utf8.(they are converted
by the upgrade procedure!!)
but the subject data now present as “???” in browser.

if I key-in new data in rt 3.8.0, they look like rt 3.4.5:
the subject data in database is encoded, not utf8.
they can show correctly as utf8 in browser.

in fact, i like my data as utf8 in database, they look better.
but more important, they must show correctly in browser.
how can i fix this? maybe i should set some parameters or update
some perl modules?
thanks a lot for help!!