You can embed QML KCMs inside applet settings windows, which is very cool and useful. However if an embedded QML KCM uses the multi-page infrastructure, kcm.push() invocations have no effect, so sub-pages become inaccessible.
This causes us to be unable to embed KCMs using this architecture into settings windows. CUrrent examples include the Notifications and Audio KCMs.
See blocked bugs for examples of the issues generated by this.