Krita crashes if you select an empty space/slot in the Color Palette docker.
Created attachment 106400 [details] (GDB report) I can confirm this also on Ubuntu with Krita 4.0 pre-alpha.
Created attachment 106401 [details] (Video example)
This is probably fixed in master already, as I ended up fixing like a dozen tiny crashes two days after the release of the pre-alpha. https://phabricator.kde.org/R37:5f7c93d7f7b4e58b06c290e9a7307a3200b295cf Please check a nightly or the next development build to check if this is gone. :)
Great! Let's close this and re-open if it recurs.