I did not do anything special, but at some point I realized that my RAM is unusual full. Mac HG is taking 1.8 GB of RAM and I do not have any idea why. Maybe it is connected with the following: I clicked on a folder an Mac HG started to calculate the differences. This took about 3 minutes of 100% CPU (Core i5 @ 2,4 Ghz) and there was not that much content in the folder.
Issue #317 resolved