Dell U2715H flickers for the inversion test

I got a new Dell U2715H monitor, I tested it here:

Lagom

Square 4a flickers quite strongly. I also tested a Benq TN monitor, that one too shows flicker for 2a, 4a, 4b.

What does that mean? How relevant is that test? Should I return the monitor? I am mostly interested about possible eye fatigue because flicker, that is why I got a flicker free screen. But it seems there are at least two kinds of flicker: PWM flicker and now inversion flicker.

5) Post your issue and all of the following data
Reason line = Monitor model, short issue description
Dell U2715H

* What is the 20 digit alpha-numeric monitor serial number and A0x revision?
CZ-0GH85D-64180-6CN-1LJS

Revision A03

* To what computer model is the monitor attached? Desktop, Intel Celeron

* What video card/GPU is in the computer? MSI GTX 1050

* What video out ports are on the video card/GPU or computer? HDMI 2.0, DP, DVI

* List all monitor cabling attached to the computer and the ports they are using: HDMI 2.0, with HDMI 2.0 cable

* What Windows power plan? Example = High performance, PCI-e Link State Off: High performance

* Press the monitor Menu button to open the monitor OSD (On Screen Display). The bottom of that screen should show a resolution. What is listed? 2560x1440, 60Hz

* Was the monitor purchased directly from Dell or some reseller? Reseller