How can milestones be "in progress"?

Simple question: if a milestone has *by definition* no duration, why is it possible to mark it as "in progress"? 

This is especially glaring in board view where there is no visual difference for milestones: they are simply included in the list of cards like any other task, and so can be manipulated like any other task. 

But milestones aren't tasks; they are decision points, markers of project phases, deadlines for significant deliverables etc. As such they should have different behaviour. 

Similar post here: https://help.wrike.com/hc/en-us/community/posts/360016651154-Why-should-I-use-Milestones-?input_string=Why%20can%20milestones