[BUG] Incorrect tab behavior in column mode

[rddim]

Is there an existing issue for this?

• I have searched the existing issues

Is the issue reproducible in Notepad++ without plugin?

• I have tried Notepad++ without plugin

Is the issue reproducible in portable version of Notepad++?

• I have tried portable version of Notepad++

Does the issue affect SciTE?

• I have tried SciTE

Description of the Issue

Using tabs in column mode breaks some of the lines that start with a tab or space.

Steps To Reproduce

1. Start 1st line with some text
2. Start 2nd line with one tab key and add some text
3. Start 3rd line with two tab keys and add some text
4. Make vertical selection (column mode) at the beginning of all lines
5. Press tab key multiple times

Current Behavior

Expected Behavior

Debug Information

Notepad++ v8.9   (64-bit)
Build time: Dec 27 2025 - 14:28:33
Scintilla/Lexilla included: 5.5.8/5.4.6
Boost Regex included: 1_85
TinyXML-2 included: 11.0.0
nlohmann JSON included: 3.12.0
Path: G:\_System\Users\Home\Downloads\npp.8.9.portable.minimalist.x64\notepad++.exe
Command Line: 
Admin mode: ON
Local Conf mode: ON
Cloud Config: OFF
Periodic Backup: ON
Placeholders: OFF
Scintilla Rendering Mode: SC_TECHNOLOGY_DIRECTWRITE (1)
Multi-instance Mode: monoInst
asNotepad: OFF
File Status Auto-Detection: cdEnabledNew (for current file/tab only)
Dark Mode: OFF
Display Info:
    primary monitor: 1680x1050, scaling 100%
    visible monitors count: 1
    installed Display Class adapters: 
        0000: Description - AMD Radeon HD 7700 Series
        0000: DriverVersion - 27.20.14540.4003
OS Name: Windows 10 IoT Enterprise LTSC 2021 (64-bit)
OS Version: 21H2
OS Build: 19044.1288
Current ANSI codepage: 1251
Plugins: none

Anything else?

1. The issue comes from b06678d
2. The last working commit is c696f6f
3. The last working N++ version is 8.8.8
4. The issue exist in SciTE 5.5.8
5. The last working SciTE version is 5.5.7
6. Maybe this can help https://sourceforge.net/p/scintilla/feature-requests/1567/