Yes, that is a new feature for 2018, to make it more confusing for everyone!

If an IRA distribution has the same amount for gross and taxable, it doesn't appear in the gross box, only in the taxable box....so 4a can be smaller than 4b.   Its weird, but correct.    If you look back at 2017 it does the same thing, BUT IRAs and pensions were on separate lines, not combined, so it didn't look so weird.