Since my mouse sits right next to my tablet, I am going absolutely mad because whenever I bump my hand into mouse4 or mouse5 there's a solid chance that my brush will just disappear. To replicate this issue simply open krita, select the brush tool, then press mouse5 or mouse4 and see what happens. It's a real pain, especially since I can't find any indication of this being an intentional keybind so I can't unbind it, and when it does happen I have no idea how to make the brush appear again.