The world is not perfect

Software contains defects. This problem is not yet solved. If you know the perfect solution that guarantees absolutely bug-free software, you should apply to Nobel prize. Otherwise, take it easy and help us to improve GanttProject testing it and submitting bug reports when you detect a defect. Consider the time you lose on detecting a bug and submitting a report as a price that you pay for using GanttProject. Again, the world is not perfect and nothing is absolutely free of charge.