output data type of fix point Add/sub block

My SIMULINK Add/Sub block performing

c=a+b.

As shown below

Data type of "a" and "b" is sfi(25, 17) whereas

data type of output "c" is here sfi(32, 17).

My question is how "c" output data type is sfi(32, 17) ?

It should be sfi(26, 17) as per addition rule.

Note: output data type is set to : "Inherit: Same as accumulator".

Thanks........