How to correctly change the passphrase of GPG's secret key?

I'm trying to change the passphrase of my GPG's secret key. I actually changed it using seahorse (Also tried gpg --edit-keys and passwd, but when I tried to export my private key it asks me for two passphrase now (Both new and old one) and uses the old one for sub secret key. Now I have to remember two complicated password! What is the correct way to change the passphrase of GPG's secret key?