I noticed this issue while working on another feature. When there are multiple tabs inside Konsole and one is dragged outside to create a detached view
the content of the new Konsole window is initially empty until a resize or click happens.

I couldn't figure out the the exact cause, but passing a different
size in Application.cpp:

void Application::detachView(Session *session)
{
    ...
    // When detaching a view, the size of the new window should equal the
    // size of the source window
    Session *newsession = window->viewManager()->activeViewController()->session();
    newsession->setSize(session->size()); //<---- e.g QSize(400, 400)

fixes the issue at first glance. Then I looked further into what setSize does and eventually landed inside TerminalDisplay. After some playing around it worked by calling updateImage instead of updateGeometry.

1. Detach a tab
2. Now Visible