Solved
The IRS indicates that, unless you have an exceptional situation (not the case with me), you should leave line 4a blank and enter the total distribution (from Form 1099-R, box 1) on line 4b.
I'm not sure why it is showing up like that. In the instructions to form 1040, it mentioned to use line 4(a) if you had a rollover. In any case, it won't affect your taxable income or tax and I can't imagine that the IRS would be concerned about it.
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