Bug 478886

SUMMARY
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When using KDE Plasma on Wayland, certain applications that were last closed in fullscreen mode exhibit unusual behavior upon attempting to exit fullscreen. Specifically:

1. Launching these applications (like Firefox) in fullscreen mode, followed by an attempt to exit fullscreen by dragging the top bar, results in the mouse cursor snapping to the top-left corner of the application window.
2. The application window then shifts to the right relative to the mouse's position.
3. Any subsequent attempts to resize the window cause it to collapse to its minimum configured size.
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STEPS TO REPRODUCE

1. Launch an application known to exhibit this behavior, such as Firefox.
2. Set the application to fullscreen mode.
3. Close the application while it's still in fullscreen mode.
4. Reopen the same application. It should launch in fullscreen mode, retaining its last state.
5. Try to exit fullscreen mode by dragging the top bar of the application window.
6. Notice if the mouse cursor snaps to the top-left corner of the application window.
7. Observe whether the application window shifts to the right, starting from this top-left corner, and does not align with the mouse's position.
8. Try to resize the application window.
9. Check if the window collapses to its minimum size.

OBSERVED RESULT

The mouse cursor unexpectedly snaps to the top-left corner of the application window when attempting to exit fullscreen by dragging the top bar.
The application window shifts to the right relative to the mouse's position, starting from the snapped top-left corner.
Any attempts to resize the application window result in it collapsing to its minimum configured size, instead of resizing as expected.

EXPECTED RESULT

When exiting fullscreen mode by dragging the top bar of an application window, the transition should be smooth. The mouse cursor should remain in the position where the drag action was initiated, without snapping to any corner of the window.
The application window should move in sync with the mouse cursor during the drag action. There should be no unexpected shift or displacement of the window in relation to the cursor's position.
Resizing the window after exiting fullscreen should be fluid and responsive. The window size should adjust according to the drag action used for resizing, without collapsing to the minimum size unless explicitly resized to that extent.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: ArchLinux 6.6.7-273-tkg-linux-tkg-eevdf
KDE Plasma Version: 5.27.10
KDE Frameworks Version: 5.113.0
Qt Version: 5.15.11