SUMMARY

After updating to Plasma 5.26.1 from 5.25.5, when a window's colours are inverted via KWin's "Invert Window Colours" or the "Invert Effect" (please note, this is *different* from the "Invert Screen Colours" effect), the window colours temporarily revert to the normal ones when the window is moved or resized. This happens only if the "Wobbly Windows" effect is activated. This did not happen in 5.25.5 (the window was wobbly without the colours reverting to normal). 

As you may imagine, this is quite distracting and unpleasant, as there are colours flashing about every time an inverted window is moved.  

Disabling the "Wobbly Windows" effect seems to fix the issue, so I guess there is something amiss when the two effects are combined.   

STEPS TO REPRODUCE
1. Invert a window's colour's  via an appropriate KWin shortcut OR use the "Invert Effect" (but not the "Invert Screen Colours" effect)
2. Ensure "Wobbly Windows" effect is activated.
3. Move (either by dragging the toolbar or via the "move" modifier key) or resize the window.

OBSERVED RESULT
Window colours revert to normal while the move / resize operation is taking place. The window returns to its reverted mode once the move / resize operation is complete (e.g. mouse button has been released)

EXPECTED RESULT
Window colours should remain inverted during the move / resize operation. 

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: OpenSUSE Tumbleweed
(available in About System)
KDE Plasma Version: 5.61.1
KDE Frameworks Version: 5.99
Qt Version: 5.15.6

ADDITIONAL INFORMATION

The "Invert Screen Colours" effect mentioned above (which is different to the "Toggle invert effect"), which also inverts the whole screen, does not seem to trigger the bug. 

If I recall correctly, Nate Graham mentioned at another instance that one of the effects is built-in, while the other is a "desktop effects" version (not sure which is which, though). 

Also, moving the window via the "Meta+arrow key" route does not seem to trigger the effect either (the inverted window is moved without any colour change triggered. It is also not triggered during the "maximise" animation that happens when "Meta+PgUp" is used to maximise the window.