Steps to reproduce:
- Start QCAD
- Switch to another application by clicking on its title bar
- Switch back to QCAD by clicking on its title bar
- Without any further clicks, start panning using the middle mouse button (panning is performed but graphics view does not update)

Alternative:
- Start QCAD
- Draw a line
- Start line parallel tool
- Switch to another application by clicking on its title bar
- Switch back to QCAD by clicking on its title bar
- Without any further clicks, try placing the parallel (no preview is shown, a click will place the parallel, graphics view is often updated much later)