Konqueror does not display any text typed in text fields/areas nor changes in html widgets while focus is on them

Using:
KDE Frameworks 5.29.0
Qt 5.6.2 (built against 5.6.2)
The xcb windowing system

I just upgraded Konqueror to the latest, using the new rendering engine.
I am forced to temporarily use seamonkey for everything because typing text in any form field does not display the text being typed. The text is however properly submitted when submitting the form. The text typed is also revealed only when the text area or text field looses focus.
The same problem occurs with other HTML widget. For example, selecting a radio button does not show that the radio has been selected until the form is submitted.

The result is that konqueror can only be used for passive browsing. Any use of forms is rendered completely impractical.