Shape_Area ?

Question re: Shape_Area on Intersect output

While in ArcMap, if I direct the output of the Intersect tool to "in_memory", why is it that the "Shape_Area" and "Shape_Length" fields on the output layer table are both set to Null for all rows?

If I do same on disk these fields are auto calculated.

Reason I ask is that I was automating this in python and made the assumption that "Shape_Area" would be updated based on Intersected polygon properties.

Is this a bug or can someone set me straight (or provide best practices) on when to assume "Shape_Area" and "Shape_Length" fields are created/updated with respect to overlay tools?

Is there a simple and fast way to update these fields while in_memory?

Thanks so much, b