I installed QGis 2.18 (64bit and 32bit versions) and i started a session with GRASS 7 in Windows 8 environment (the same thing I did on another workstation with Windows 10). I loaded a test layer with a shpfile with a few elementary polygons. Some polygons overlap for small areas. I imported the layers in one location and created a Mapset. The topology appears created correctly after my cleaning work. All goes well apparently. At one point QGis starts producing in the directory "PERMANENT \ .TMP\UNKNOWN \" an infinity of 512Kb files that paralyzes the harddisk (100% use) and freezes the session. In particular, if i try to populate the Mapset with new centroids or breaking lines. When I stop the session and i reopen the project in a new session, the Mapset is corrupted. I tried the same actions with other polygonal files or different linear files, always the same thing happens. I wonder if it has already been seen this QGis behavior.