I have however, a few times been tripped up by undo/redo.
It seems as though if you make a change, use tab to indent a block of text, make another change and then attempt to undo, you cannot undo further back than when you did the tab.
That's pretty much reproducible all the time.
What's less common, but more serious, is I've see undo / redo only correct partially what it should have done.
This has left me with entire blocks of template code disappearing, incomplete bits of code reappearing and then be unable to do the mess using undo/redo forcing a reload of the template potentially losing changes... Luckily I can now Ctrl+S every few seconds