Hi, thanks for the suggestion! Actually repaint() causes a repaint immediately, which is what might be causing the problem.
But in looking at the docs again, I wondered why I'm even calling updateGL() directly. Changing this to update() causes the new QGLWidget version to behave like the old version, which solves my immediate problem.
It seems to me now, though, that all versions are overloading something, probably message handling, as the UI is sluggish. If I have time, I might look at moving gl rendering to a separate thread to keep the UI responsive.
Thanks again!