Imagine having a large image such as CT_LiverLarge_3D and creating some multi labels. Whenever you as much as click on a label (which changes the active label -> calls modified) the whole image statistics calculation pipeline is triggered, which will cause all your core to run for a good 20-30 seconds. Although this does not freeze your system you get a noticeable slowdown.
We should govern image statistics calculation differently that we currently do. I propose a checkbox in the image statistics plugin that enables/disables automatic updating of the statistics to prevent the above mentioned problem. A disabled checkbox should trigger a warning message of the image/mask that is connected to the calculator has been modified but the statistics have not been updated yet.