MacVim incerts dot on a double space

Steps to reproduce

1. Open new file and enter insert mode
2. "a b" (2 spaces)
3. Observed: standard macOS replacement would be in place "a . b"

Issue is GUI-specific as too much "modernisation" in place

Expected behaviour

I'll see "a b" on a screen

I'd expect also a regression test for this case.

Version of Vim and architecture

arm64

Environment

macOS 12

How MacVim was installed

Github

Logs and stack traces

No response

Vim configuration where issue is reproducable

No response

Issue has been tested with given configuration

• by running MacVim.app from GUI macOS interface
• by running vim/gvim/etc installed by MacVim
• by running other versions of vim (e.g. /usr/bin/vim)

Issue has been tested with no configuration

• by running mvim --clean (or gvim, supplied by MacVim distribution)
• by running vim --clean (in terminal, supplied by MacVim distribution)
• by running vim --clean (in terminal, other suppliers, e.g. /usr/bin/vim)

Other conditions

• The both Homebrew packages "vim" and "macvim" are installed

Start by reproducing the behavior with MacVim.app or mvim --clean, then compare it with vim --clean in the terminal as described. Locate the MacVim GUI path responsible for the double-space behavior and add a regression test confirming that a b remains unchanged on screen.