Brush size changes between versions of Illustrator

Question

I hope someone can help me. When I open a AI doc in Illustrator v CS6 the brush definition says 1pt round and the size is 1pt in the settings. When I open the same file in AI CC, the brush says 1pt round, but in the settings, the size is now 0,8pt.
I am struggling to understand how this happens. Any ideas? Thanks!