[Solved]: What's the problem of ClickToFocus?

My window focus policy:

Style * ClickToFocus, MouseFocusClickRaises

It functions well in about 10 minutes after I start FVWM, windows get focuses and raise by mouse clicks. After that short period, it just stop working. When I hit the mouse on a window, the title bar stays in inactivate mode, the input focus still belongs to previous activate window, and the window doesn’t raise.
However, I still can focus a window by click on my taskbar, which calls “EWMHActivateWindowFunc” function. Close or inconify a focused window will also release the focus. And newly started applications get the focus without problem.

BTW, I tried

 Style * ClickToFocus

but the problem is still there.

I also have some windows “NeverFocus”, but I doubt this matters.

It’s so annoying, any input is appreciated, Thanks!

Edit: Found where the ache comes from.
For anyone has the same problem:
Why do NumLock, CapsLock and ScrollLock interfere with ClickToFocus and/or my mouse bindings?