Why does it say OS change

Trying to learn and understand. I'm sure some of the knowledgeable members here can explain this to me.

Noticed earlier this week that when the map characteristics are changed. The "change history logs display a change in the OS as well=code modification? [even though I have not changed the OS or installed the speed density 2bar patch]. Just modified the MAP data
WHY? Is something else changing in some table? Is the OS somehow changing? Am i now suppose to now write entire? and not just calibration?

here is a screenshot of what it shows. (ignore the value I entered- its just to show how it changed)