Turbo tax is not calculating my 1099R disaster distribution correctly, says 1/3rd of 30k is 20K

I paid tax on 10K of the 30K I removed. I should pay tax on 10K this year and the final 10K next year.  Turbo tax says 1/3rd of 30K is 20K. I can change the 1099R taxable amount to 10K but I don't think this is correct or legal