Sidebar tab UI breaks when dragging tab to pinned area during Glance preview

[0Ky]

Captchas

• I have read the instructions.
• I have searched existing issues and avoided creating duplicates.
• I am not filing an enhancement request.
• I have checked that this issue cannot be reproduced on Mozilla Firefox.
• I have checked that this issue can be reproduced once I removed all my Mods and Custom CSS.

What happened?

When using the Glance feature in a pinned tab, dragging a normal tab into the pinned area (via mouse drag-and-drop) causes a UI issue in the sidebar. The layout visually corrupts, making it appear as though two tabs are merged into a split view. However, the dropped tab disappears completely and becomes inaccessible. It will reappear as a pinned tab once you restart the browser.

In some cases, the issue escalates, the pinned tab becomes completely unremovable, with the Close Tab button no longer functioning.

This does not happen when pinning a tab via right-click/context menu, only with mouse drag-and-drop.

Steps to Reproduce

1. Visit any website and pin the tab.
2. Alt + Click a hyperlink to open it in the Glance view (preview overlay).
3. Drag a normal tab (not pinned) and drop it into the bottom-most area of the pinned tab section.

Expected Behavior

• The tab should be pinned cleanly without breaking the layout

Additional Notes

• This bug is also reproducible in version 1.11.1b, on both Linux and Windows.
• The issue only occurs when using mouse drag-and-drop.
• It seems to be triggered specifically while a Glance preview is active in a pinned tab.
• Dragging and dropping a normal tab into the bottom-most area of the pinned tab section only causes the tab in the sidebar to break.
• Sometimes the affected pinned tab becomes resistant to standard close/remove buttons.

Video Demonstration

Zen-Tab-Bug3.mp4

Version

1.11.2t

What platform are you seeing the problem on?

Linux (AppImage), Linux (Flatpak), Linux (Tarball), Windows - x64, Windows - aarch64

What component is this issue related to?

Tabs

Relevant log output if applicable

[sporocyst]

Can confirm

[Propheticus]

Confirmed on 1.11.2b (and latest twilight).
Nice and clear description @0Ky !