The bug is caused by: 1. Close the game inside a level. In that case, some unlock progress is missing. But the line progress is still there. Visit locked levels should unlock them. 2. Draw on a board of large width (7-3-8 and 8-?-3). In that case, the game crashes on saving and save file is lost. If you can find a file named "understand_old.sav" in your game folder, rename it to understand.sav. It should restore your progress before yesterday's update. If you want to restore more progress, you may modify the save file by: [spoiler] First, make a backup. (Never forget to make a backup when modifying is what I just learnt) Open it with notepad. The level names within the first pair of square brackets are your solved levels. ? levels are named as EX instead. (For example, 1-? as EX-1) Just add what you need. An example: [["1-1","1-2","1-3","1-4","1-5","1-6","1-7","1-8","1-9","1-10","EX-1"], (followed by your last visited level, version number of the game, saved lines, and many others) [/spoiler] Sorry for the trouble. My bad programming and testing habits should be blamed. I'm making a test tool to avoid future mistakes like this. To show my apologies, a free chapter update will be available in next month.