I cannot find any official information which would support how Turbotax is doing the calculation (sum of all max values). Logic, how the actual form questions stands ("Maximum value of all deposit accounts") and conversation with IRS which is mentioned by user "Hmmmmmmmmm" above strongly suggest that Turbotax is doing wrong thing and refuses to correct the error.
Probably IRS lets it go as this is not the most important field on the form anyway but it seems that it's is simply wrong.
