BUG. Proportional Editing

Blender 2.9. In edit mode.

1. I turn on proportional editing with the O button. I use its functions.
2. Disable it with O button. Select any vertex and try to move it with the G button, proportional editing turns on by itself, without my participation.
3. Disable it again with the O button. Now when I move the vertex, everything is fine, proportional editing is not enabled.

This is very annoying. Impossible to work.

It also happened that I turned on proportional editing, tried to move the vertex, and proportional editing turned off by itself. It turned on for the second time.