MacVim selects one letter more to the right when selecting by mouse

Steps to reproduce

1. write text
2. put cursor in the middle of the word
3. select backwards few letters by clicking mouse
4. One letter more to the right has been selected

Screen recording with --clean parameter

https://github.com/user-attachments/assets/df0712a1-63de-4231-8d8f-b7c1bb2ccd0a

Expected behaviour

Other editors, input fields and terminals doesn't exhibit this behaviour. They select exactly the text requested to be selected.

I've tried: Notes.app, Terminal.app, Kitty, Alakritty, VSCode/VSCodium, Jetbrains editors, chat apps, various browsers

Screen recording from Notes.app

https://github.com/user-attachments/assets/8b10f823-66a6-46fc-a2cf-31ae5adb1bbb

Version of MacVim

MacVim r182 (Vim 9.1.1887)

MacVim installation method

GitHub releases

Environment

macOS Version: 15.7.2

Logs and stack traces

Vim and MacVim configuration where issue is reproducable

No response

How was MacVim launched?

• by launching MacVim.app in macOS (by using the Dock, Spotlight, or the open command)
• by running mvim/gvim in the terminal

Issue has been tested with clean configuration

• by running mvim --clean (or gvim, supplied by MacVim distribution). You can also use the File → "New Clean Window" menu item within MacVim.
• by running vim --clean (in terminal, supplied by MacVim distribution)
• by running vim --clean (in terminal, other suppliers, e.g. /usr/bin/vim)

首先，在 macOS 15.7.2 上使用 --clean 复现 MacVim r182 中通过鼠标向后选择的行为，然后将其与终端 Vim 的行为以及提供的编辑器录制进行比较。当通过鼠标向后选择时恰好高亮所请求的字符，且不包含右侧多出的字符时，即可视为完成。