I have just added a keyfile and was doing some testing

On adding a master password and keyfile I copied the keyfile to a usb drive and unplugged drive. Changed master password with the original keyfile. quitted enpass and restarted it. Plugged the usb drive back in and selected the keyfile on the usb drive (old password) and used my new master password and enpass logged in.

Is this normal or should it be a new keyfile after the master password as changed? 

Hi @APC

Welcome to the Enpass Forums.

A Keyfile is basically a file on your computer which contains an encryption key, and when used along with a password, it acts as a second factor of authentication. If you change the master password with an active keyfile, Enpass will require the new master password and the same keyfile next time you log in, unless you remove it and change the keyfile manually while changing the master password.

The user is also notified about it when trying to change the master password with an active keyfile (please refer to the below screenshot) -