I started experimenting with tiki at 4.x and I am currently running 8.3. I somehow messed up the header and now the login button has no space above it and is cut off by the top of the browser.
I did not modify any templates or CSS so all the changes were made by some settings. I am using Fivealive for my theme. The issue persisted through the last couple of upgrades so I know it is something in the database that needs to be changed.
You can see the problem here