Yes, that's how delegations work, if you change the amount then you're editing the current delegation and the difference goes into the 7 day return process.
You can see your current delegations at https://steemworld.org/@schubes if you go to 'Delegations (Out)'
In this example you started with 10SP, edited it to 15SP, then the second edit down to 5SP, so as I understand it 10SP will return to your account in 7 days and 5SP is delegated to umich as of this post.