I just found out what caused that BUG I mentioned a couple of weeks ago: when I press the SHIFT key to be able to create a complete line, sometimes the preview line does not appear; it seems that the absence of this preview line, changing the frame and try to create the whole line, is the cause of this BUG. I hope this is the correct cause of the BUG and I also hope to be helping to improve this fantastic program :) !