Time Machine - no incremental backup of VM?

Hello everyone!

I wonder, what I am doing wrong: Since I am using Parallels Desktop, every Time Machine backup takes ages as around 8GB are written on the backup HD every time. I read in the knowledge base:

"Parallels Desktop for Mac includes improved integration with Time Machine. When your machine is backed up, only the most recent changes are saved (the latest snapshot), so the backup process takes less time and uses less space on your Time Machine storage device."
(https://kb.parallels.com/8827)

Obviously that doesn't work in my case and Time Machine makes a complete backup of the VM file every time. I have Smart Guard off.
Can anyone help?

 

Update: Every Time Machine backup takes actually around 60 GB (not 8).