Hi Marcel,
the issue of windows being invisible when dragged in the new VM is a major bug. The VM needs to be backwards compatible. It souldn't break old images. So we need to find a way of restoring the default behaviour in images that don't set the relevant preference.
To reproduce take e.g. Squeak 6.0 alpha or the ;ast of the 5.x line and simply try and move a window about As soon as the window starts to move it disappears and then reappears when the mouse button is released. This must be fixed. _,,,^..^,,,_ best, Eliot