I spend many hours trying to find out what is wrong but I am at a loss now. Everytime I decide to make a custom UI and assign it to a hotkey all the tool palette items will simply dissapear! It is driving me a bit crazy.
Some googling showed me that this problem occurred in Zbrush 4.2 and was supposedly fixed. Maybe this file still works but even if it would it does not seem to be online anymore.