Now that we have that beautiful standard KMessageWidget Okular should use this one rather than its custom implementation. This gives us a unified look and feel, and also they transition in beautifully :) Reproducible: Always
Kate now also uses a free-floating KMessageWidget derivate.
It now does!
Uh, more than "now" - this bug was strangly missed during the Okular sprint (long time ago) when it was fixed.