Description:
I’ve noticed for a while that drag-and-drop does not work as reliably on Linux Mint Cinnamon as it does on Windows. When selecting text, then clicking and holding to drag it downward, the text is not carried. Instead, Writer starts a new text selection, as if the original selection had never existed.

What made me suspect this is a real bug is that increasing the drag-and-drop threshold in Cinnamon’s settings makes the problem even worse. Conversely, setting the threshold to 1 pixel makes the issue disappear completely.

After testing on multiple computers and through various distros on DistroSea, I found that the issue affects all desktops using GNOME technologies (GNOME, Cinnamon, Xfce), but does not occur on KDE Neon.
There is no issue in LibreOffice Calc either.

Later I realized this correlated with the VCL: KDE uses kf5, while GNOME-based desktops use gtk3. This points clearly to a gtk3 VCL regression.

If I run Writer with the gen VCL backend, the bug disappears. But this breaks Nemo integration when saving files. Removing the libreoffice-gtk3 package also works, but is not an ideal workaround.

Steps to Reproduce:
1 Open LibreOffice Writer under a GTK3-based desktop (GNOME, Cinnamon, Xfce).
2 Ensure the system’s drag-and-drop threshold is higher than 1 px.
3 Select a portion of text.
4 Click and hold on the lower edge of the selection.
5 Drag the cursor downward, crossing into the next line before exceeding the drag-and-drop threshold.

Actual Result:
The text is not dragged.
A new text selection is created instead, as though there had been no initial selection.

Expected Result:
Dragging should move the selected text, regardless of the drag-and-drop threshold, as it does in KDE (kf5) or in Calc.

System Information

Affected VCL: gtk3
Unaffected VCLs: gen, kf5
Desktops tested (affected): GNOME, Cinnamon, Xfce
Unaffected desktop: KDE Neon, Windows
LibreOffice apps tested:
Writer → affected
Calc → not affected
Workarounds tested:
Running SAL_USE_VCLPLUGIN=gen lowriter → works

Additional Notes:
The issue clearly appears when the cursor crosses into the next line before the drag threshold is reached. Lowering the Drag and Drop threshold in OS mouse options to 1 pixel makes drag-and-drop behave normally, which strongly suggests incorrect handling of movement events in the gtk3 VCL.
Drag and Drop works perfectly on any other app like Cinnamon's text editor