mvia to thruvia DRC missing

Hi

I am having difficulty getting a DRC to occur when I stack a microvia on top of a thru via.  If the mvia is not stacked then the DRC is getting flagged if it's on the edge of the thru via.

However, when the mvia is coincident with the thru via the DRC goes away.

I *think* I have the DRC setup correct for Same Net checking but am puzzled as to why the overlap is allowed.

Any hints on how to flag overlap of thru to mvia?

Thanks