"What-if" for MFJ vs MFS numbers do not add up

Trying to compare MFJ and MFS following this tip 

 

However, for line 62 (total tax) or 72  (refund/due), 2nd column (joint) does not match 1st column (current filing, which is joint).  It should be exactly the same since both are joint, shouldn't it?

 

It also does not match the sum of column 3 and 4, which are the what-if individual filings.

 

So, what is column 2 (joint) exactly? Is this what-if worksheet of any use?