I have not found a similar problem mentioned in this forum, so I hope I'm not repeating an existing topic.
I have been using QCAD for a short while only, and everything seems to work OK. But this morning I discovered that when I try to use tools such as 'chamfer/bevel' or 'lengthen', the mouse pointer disappears from the drawing area.
Here is a specific example: I have a rectangle, and I want to chamfer one of the corners. So, I click on 'chamfer/bevel' and enter the distances in the Options toolbar. I now have to select the entities, but as soon as I move the mouse pointer into the drawing area, it disappears, so that I cannot select the entities. The same thing happens when I try to lengthen a line using the 'lengthen' tool.
Ubuntu 9.04, QCAD 18.104.22.168 Professional