Thank you so much for your advice. Here is what I am going to solve this problem:
1. In 1099R-line2a<taxable amount> subtract the adjustment to avoid double-taxation with explanation.
2. In 1099R-line1<gross distribution> subtract the adjustment with a note: "
To avoid double-taxation,this adjustment should be subtracted from <taxable amount>. But there is a Turbotax software bug which mistakenly links 1099R-Line1(gross distrib) into 1040-Line4a(taxable amount), instead of 1040-Line4b(taxable amount) as it should. So 1099R-Line1 also has to be subtracted for the adjustment (Turbotax filing only)"
wc
