Sorry for my confusing message --- I know what has happened.
Another package I used, `libertine` in this case, has the following:
> \def\bfseries@rm{b}
Since CJK only declares boldface extended `bx`, the medium weight `m` is used.
It has nothing to do with TeX distributions. As far as I can see, older distributions
have the same issue with CJK being used with other fonts.
The CJK package assumes the default value `bx` will be used and does not provide
an explicit substitute, so using CJK in conjunction with other fonts that change the default
breaks `\textbf{...}` in CJK.
Now I wonder if adding substitutes explicitly by
> \DeclareFontShape{C70}{bkai}{b}{n}{<-> ssub * bkai/bx/n}{\CJKbold}
to c70bkai.fd and other .fd files is a proper solution. And, is the CJK package still
accepting any new contributions?
Cheers,
Liang-Ting