Chinese input not work in embedded Sametime 9.0.1 on Mac Yosemite

I just installed the IBM Notes 9.0.1 64bit version on my new Macbook Pro (Yosemite). But I cannot input any Chinese character in the embeded Sametime.

Only using Chinese Input Methods in embeded ST has problems, and all other applications, such as calendar/mails, work fine.

Please advise, thanks.

Notes version:

IBM Notes 9 Social Edition

Release 9.0.1 (64-bit)

Revision 20150916.0754-EXT (Release 9.0.1 (64-bit))

Standard Configuration

L-GHUS-9Z3KRF

Sametime Plugin version:

9.0.20150916-0754

Subject: root cause is some specific IME

I figured out that the root cause is the new IME I just installed, Yahoo KeyKey IME. Yahoo! 奇摩輸入法 (Yahoo! KeyKey) v1.1.2535 最終版-文書編輯、PDF-【狂人論壇】 http://123.briian.com/forum.php?mod=viewthread&tid=577

Uninstalling YahooKeyKey and everything works fine now. However it’s very strange because all other applications do not have this problem, only Notes.