If NumLock is on, mouse clicks no longer change focus from one window to another. The window in which the mouse is clicked pops to the top on the desktop but the window does not receive focus. Turn off NumLock and proper operation is restored, i.e., mouse clicks move the focus to the window in which the mouse was clicked.
This is not actually a bug, more of a feature. This was created for people who wanted to play Doom and Quake type games and not have the color map keep changing on them if their pointer exited the window. This only usually is set as default in fvwm. You could try another window manager to alleviate the problem.
Some X applications support the use of the keypad keys. These are enabled when NumLock is on. The keysyms generated when NumLock is on are KP_1, KP_2, etc. Choosing the PC NumLock key to turn on the "feature" of disabling the setting of focus via a mouse click clearly disrupts the proper function of the mouse on the desktop for those who are using X applications which support the use of these keypad keys. It would have been better if the choice of key where selectable via an fvwm X resource attribute. Indeed, setting this attribute to a key (or not) could also double as a way to enable (or disable) the feature. In any case, leaving things as they are means fvwm has a useful feature for players of doom and, at the same time, an annoying bug for users of applications which support the keypad keys.
This is the documented behavior of X. Also, this is not something that Red Hat has control over, as it is a feature of X and not something that Red Hat chose to implement.