I have tried the stc sample within the official wxWidgets master source code, it has the same issue.
In my opion, C:B can be better then the sample which is just a demo, C:B is a production.
I will use C:B as my daily working IDE.
And, I tried fcitx, it works fine with C:B.
If so, I am giving up the original input method tool, scim, I used it up to dozen years, and switch
to fctix.
Also, hope C:B to be better and better.