User Account Control starting TeamViewer QuickSupport

Hello,

One of our customers is using TeamViewer QuickSupport. They have User Account Control with user credentials enabled on their clients.

Everytime the start TeamViewer QuickSupport, a UAC login screen pop ups and the neet to fill in their credentials. After filling in their credentials, QS will start.
But if the just close the UAC login screen without filling in credentials, QS will aslo start without logging in to the UAC prompt.

Q1: is it possible to start QS without getting an UAC prompt?
Q2: why will QS start without giving permissions in the UAC prompt?

I hope somebody can help me.