Kate has no window borders, and thus no minimize, maximize, and close buttons

This will happen if you:

• right click on the kate window border or it's entry in the task manager bar
• select 'more actions' -> 'Full screen'

or

• press ctrl-shift-F

I originally solved this by:

• removing katerc from ~/.kde/share/config

This is best undone by:

• pressing ctrl-shift-F