Description:
I cannot reorder slides in LibreOffice Impress.

Interestingly, I found that the environment variables QT_QPA_PLATFORM, SAL_USE_VCLPLUGIN and GDK_BACKEND can influence the outcome.  I am running KDE Plasma with Wayland.  I'll elaborate the results in each combination of the env vars.

Steps to Reproduce:
1. Open libreoffice
2. Create three slides, with titles "aaa", "bbb" and "ccc" in that order.  I added the titles just for identifying those slides.
3. Save it as "reorder-example.odp" so that we can open the same file and try different combinations.
4. Inside the "Slides" side bar on the left, move the mouse cursor onto the slide "aaa", press and hold the left mouse button.
5. Start moving the mouse.
6. Move the mouse to the gap between the slides "bbb" and "ccc".
7. Release the left mouse button.
8. Close the Impress window.  Do not save if asked.

Then restart Impress with the following commands, and repeat step 4 to step 8

-   QT_QPA_PLATFORM=xcb libreoffice reorder-example.odp
-   SAL_USE_VCLPLUGIN=gtk4 libreoffice reorder-example.odp
-   GDK_BACKEND=x11 SAL_USE_VCLPLUGIN=gtk4 libreoffice reorder-example.odp

(Note: Since I am using KDE Plasma Wayland, Qt and GTK will use their Wayland backends by default unless overridden by QT_QPA_PLATFORM and GTK_BACKEND).

Also try moving the slides in the "Slides Sorter" view in each combination.

Also try moving slides by right-clicking the slide -> "move" -> "slide down".

Actual Results:
With bare "libreoffice" command,
-   After step 5, the mouse cursor becomes the prohibited sign (like the Unicode character "🛇" (U+1F6C7)).  This doesn't look right.
-   After step 6, a rectangle with "1" in the middle appears between the slides "bbb" and "ccc".
-   After step 7, "aaa" is still the first slide.  The order of the three slides are not changed.
-   Step 8 does not ask me to save the file.

With "QT_QPA_PLATFORM=xcb libreoffice reorder-example.odp"
-   After step 5, same as above.
-   After step 6, same as above.
-   After step 7, "aaa" is successfully moved between "bbb" and "ccc".
-   Step 8 asks me to save the file.

With "SAL_USE_VCLPLUGIN=gtk4 libreoffice reorder-example.odp"
-   After step 5, it crashes immediately, with the log message in the terminal: "Gdk-Message: 23:46:49.286: Error 32 (Broken pipe) dispatching to Wayland display."

With "GDK_BACKEND=x11 SAL_USE_VCLPLUGIN=gtk4 libreoffice reorder-example.odp"
-   After step 5, same as when using the bare "libreoffice" command.
-   After step 6, same as when using the bare "libreoffice" command.
-   After step 7, the slide "aaa" disappears.  Only two slides, namely "bbb" and "ccc", are left in the document.  Pressing CTRL+Z will make "aaa" appear again.
-   Step 8 asks me to save the file.

Dragging slides with mouse in the "Slides Sorter" view behaves exactly the same as in the "Slides" left side bar in all env var combinations.

The "context menu -> move -> slide down" approach works in all env var combinations, even with "SAL_USE_VCLPLUGIN=gtk4 libreoffice reorder-example.odp" which crashes if I drag the slides.

Expected Results:
Step 5: the mouse cursor should be a "hand" icon instead of a "prohibited sign".

Step 7 should successfully move the slide to the right position.

It should behave the same in the "Slides Sorter" view.


Reproducible: Always


User Profile Reset: Yes

Additional Info:
Help - About LibreOffice: (Note that the "SAL_USE_VCLPLUGIN=gtk4" env var will change "VCL" to "gtk4".)

Version: 25.2.3.2 (X86_64) / LibreOffice Community
Build ID: 520(Build:2)
CPU threads: 32; OS: Linux 6.14; UI render: default; VCL: kf6 (cairo+wayland)
Locale: en-US (en_US.UTF-8); UI: en-US
25.2.3-3
Calc: threaded

Some more information:

Linux distribution: ArchLinux
packages:
-   libreoffice-fresh: 25.2.3-3
-   qt-base: 6.9.0-2
-   plasma-desktop: 6.3.5-1
-   kwin: 6.3.5-1
-   gtk4: 1:4.18.5-2
-   wayland: 1.23.1-2
-   xorg-xwayland: 24.1.6-1