Pinned and Folder tabs duplicate when split

[yogi1308]

Preliminary Checks

• I have read and understood the important section above.
• 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?

1. When splitting a tab that is inside a folder with a regular tab outside any folder, a duplicate of the folder tab is created instead of splitting the original.
2. The same duplication occurs when splitting a pinned tab with a regular unpinned tab that is outside any folder, a duplicate of the pinned tab is produced.
3. When both conditions are combined, meaning a folder tab is split with a pinned tab, duplicates of both tabs are created simultaneously.
4. Similarly, splitting two pinned tabs with each other also results in duplicates of both.
   Split view works as expected only when both tabs involved are regular tabs, unpinned, and not inside any folder.
   Thank you for your attention and for contribution to this awesom open-source project
   Also I am using zen-browser-bin downloaded from the AUR.

Expected behavior

: Split view should display two selected tabs side by side without creating duplicates, regardless of whether the tabs are pinned or inside folders.

Actual behavior

Duplicate tabs are created whenever a pinned tab or folder tab is involved in a split.

Steps to reproduce

Attempt to split any combination of pinned tabs or folder tabs with each other or with regular tabs and
observe that duplicate tabs are created of the tab which was inside the folder or pinned.

Screenshots and videos

Screen.Recording.2026-03-23_20-28-13.mp4

1. Observe how in the above video the settings tab is duplicated when split with the github tab. same thing happens when a pinned tab is split with a regular tab(by regular tab, i mean a tab that unpinned and outside any folders)

https://github.com/user-attachments/assets/0fb0c459-b4c4-4599-8265-7bce4b0abdcf
2. You can see in the second video how splitting the claude and gemini tabs together creates duplicates of them both. The same thing happens when one's a pinned tab and other one is inside a folder, that is 2 tabs are created in that situation too. When both of them are in folders, no duplicates are created

Version

Mozilla Zen 1.19.3b

What platform are you seeing the problem on?

Other

What component is this issue related to?

Split View

Relevant log output if applicable

[mr-cheffy]

This is expected sorry