Leaving a static image for >30m has no visible effect on this panel.
In this case it's the flicker itself which persists on _top_ of a slight color shift, and requires only a few minutes of exposure.
I tried this on another older dell IPS panel and I observed the same. Quite interesting!
Trivia: static images on LCD can be sometimes seen as flickering because they are not really static, to prevent burn-in and subsequent damage polarity is reversed every frame. Some details here: http://www.techmind.org/lcd/
My guess is that it's down to the relationship between the specific interlacing used by the panel, if any (lagom.nl has inversion/pixelwalk tests to determine which type a monitor uses), compared to the 60Hz flickering. Something about the two together induces image retention far sooner than the average content, albeit image retention that also fades much quicker.
I left the "palette demo" flickering on the same spot for about 5 minutes while doing other stuff on a dell up2720.
After closing the page, the pattern was still visible on the LCD when showing a grey image (or on top of the same pattern again where ghosting became quite visible). It's visible both as a slight color shift but mostly flickering.
Putting the screen to a fixed color pattern (via LCD conditioning) was still showing the same, again mostly on grey, excluding thus most of the driver/display chain as an issue which I suspected as first (dirty cache).
The effect is gone after about 5 more minutes.
First time I see persistence like this on an LCD. A static flat image can't do this on this panel.
Can anybody reproduce the same?