Ubuntu 18.04 - Greeter on secondary monitor after installing Nvidia driver

Having set up a dual monitor system on Ubuntu 18.04 LTS and after having installed Nvidia display driver, I encounter the following problem:

Right after the installation of the latest stable Nvidia driver on my Dell Precision M4400 laptop, my monitors were mixed up: The stand-alone LG monitor was assigned primary monitor, the built in laptop display was assigned secondary monitor in Ubuntu settings. I corrected this plus I changed the displays' position: According to the position of the devices on my desk, I moved the laptop monitor to the left of the external LG monitor. The greeter still appears on the LG display.

Prior to the installation of Nvidia drivers this problem didn't show, the greeter showed up on the primary laptop display. Is it a bug or did I just miss some necessary settings?

Kind regards,
Frank