None of the file dialogs in KDE applications are correctly modal. This is the ID used for the WM_TRANSIENT_FOR is wrong and isn't a known xcb_window_t client (my guess it that its the root or something, but I didn't check). This violate the spec and doesn't make any sense.

Without the KDEPlasmaPlatformTheme.so QPA, the behavior is correct and compliant. With it, while the XPROPERTY is set, its value is wrong.

In AwesomeWM, I can confirm that none of the xcb_window_t clients matches the WM_TRANSIENT_FOR exposed by the plasma QPA.

Why is this important:

 * It may cause the file dialog to show on the wrong screen
 * It prevent some WM to place the dialog in the right workspace/activity
 * It breaks some WM modal dialog detection, however not all WMs are affected by this.

Reproducible: Always

Steps to Reproduce:
To reproduce, install xwininfo and use xprop

1) Using xwininfo, check the WinId of an application (like Kate).
2) Open a file dialog in the said application. 
3) Using xprop, get the WM_TRANSIENT_FOR value
4) See how they don't match

Actual Results:  
With the QPA, the WM_TRANSIENT_FOR doesn't match the "xwininfo: Window id:" row of xwininfo.

Expected Results:  
Without the QPA, the WM_TRANSIENT_FOR matches the "xwininfo: Window id:" row of xwininfo.

The bug is present in framework-integration. The bug isn't present in KDE4. I didn't test framework < 5.7, but those above it seem to have the issues.