Seems this post helps those “overstay isn’t a problem” people to learn that ANYTHING stamped or written in a passport is the business of ALL immigration and airport authorities all over the world.
And it’s exactly the business of a Singapore immigration officer who they admit to Singapore. What other purpose do they exist?
Having said that - I don’t really understand the purpose of the OP: Person with correct visa incorrectly stamped is admitted after further questioning by officials doing their job.