It is not a anomaly. Microsoft Excel retains 15 significant digits
See this https://support.microsoft.com/en-us/kb/65903

The question is more like "which is the difference between these two group of expressions?" Is not the same? Why?
=A6-B6 or =(A6)-(B6) or =A6-(B6) or =(A6)-B6
and
=(A6-B6) or =((A6)-(B6)) or =(A6-(B6)) or =((A6)-B6)

If I use in D6 =A6-B6 and in E6 =D6=0 and I get TRUE in E6
So, why I get FALSE if I use =(A6-B6)=0 ?