This is similar to https://bugs.kde.org/show_bug.cgi?id=340917 with slightly different behavior. (but moving the window is the same behavior)
System Settings→Window Decorations→I can confirm that Breeze and Plastik are both broken, while Oxygen works (easy workaround)

Reproducibility: Works the first three clicks, broken afterward.

Reproducible: Always

Steps to Reproduce:
1. Create two overlapping windows (konsole)
2a. Repeatedly clicking inside the current inactive window focuses and raises it.
2b. Repeatedly clicking the titlebar of the current inactive window focuses and raises it until about 3 clicks in (depending on what was focused when you started and how many clicks it took you to overlap the windows).

Actual Results:  
After it stops working correctly, and you've just now focused and raised one window: On the inactive one:
3a. Titlebar buttons don't change color on (react to) mouse hover.
3b. The first click is ignored, whether it's on the titlebar (doesn't focus or raise), the close button (client doesn't receive signal), or any other titlebar button (menu, shade, keep above/below, help, minimize, maximize).
4. The second click works, whether it's on the titlebar (does focus and raise), the close button (client is closed or asks to save), or the window menu opens.
The two clicks don't have to be in the same place - either one may be over a button while the other is only on the titlebar.

The speed of these two clicks matters. The first titlebar click is ignored by focus, raise, and buttons. But it counts as the first half of a double click. As a result,
A. Two slow clicks on the close button result in the first ignored, and the second closing the window.
B. Two fast clicks on the close button result in a double-click on the close button, which isn't handled. (Normally you can't double-click a close button without single-clicking it first, which closes the window before the second click is received.)
C. Two slow clicks on the titlebar result in the first click being ignored, the second click focusing and raising the window.
D. Two fast clicks on the titlebar result in the first click seemingly being ignored, the second click completing a double-click, and the window maximizing (that's the default, but I have it set to lower the window)
  D1. Also, (if your view of both windows wasn't obscured by one of them maximizing,) double-clicking on the titlebar resets the "click timer" - you must now click on the inactive windows' titlebars three times for the titlebars to start ignoring the first click again.

Expected Results:  
Changing the theme to Breeze or Plastik from Oxygen would not affect any actions - Repeatedly clicking the titlebar of the current inactive window should never stop focusing and raising it.

> cat /etc/os-release
NAME=openSUSE
VERSION="20141112 (Harlequin)"
VERSION_ID="20141112"
PRETTY_NAME="openSUSE 20141112 (Harlequin) (x86_64)"
ID=opensuse
ANSI_COLOR="0;32"
CPE_NAME="cpe:/o:opensuse:opensuse:20141112"
BUG_REPORT_URL="https://bugs.opensuse.org"
HOME_URL="https://opensuse.org/"
ID_LIKE="suse"
> I'm on their Factory release.
Breeze widget style, look and feel, desktop theme, cursor theme, and splash screen are not related to this bug - only Breeze Window Decorations.
KDE version 5.4.0
breeze 5.1.0.1-1.1-x86_64

I thank the other bug report(er) for showing me enough of the cause of the problem to see the workaround (System Settings→Window Decorations→Oxygen→Apply). I changed too much of my system at once (tumbleweed to factory, plasma to 5, themes) to see what caused it.