Yeah, the authentication/transaction password is seriously ridiculous, especially since you are already logged in and all.
In some other platform you enter the system after providing CORRECTLY
userid password+ Transaction password,hence ask NO password later.
In NOW also, it won't ask any passwords.(I think you have not changed
transaction password while changing other password.Anyhow ZERODHA is
the right person to approach.).
There is a small trick ,so that it won't ask transaction password for rest
of the DAY.(Atleast it happens in my case).
a.BUY Nifty future for say ,5000.
b.Then place a sell order 5900.
c.Then modify the order to your desired value, by giving Transaction Password.
d.Further modification will take place automatically.