Say you have a Text whose DOM element currently contains the text A. Now you enter a B, but not by pressing the B key, but via the numpad: Alt+066. (This input mode could be Windows-specific.) You'll see the text AB in the browser, as you'd expect. When you leave that input, it will revert back to A (i.e. the B gets deleted again, which is an error).

My working theory is that this is because the Text._keyUp event for the last key (6 or Alt) happens before the browser adds the input character in the DOM. Text._keyUp then triggers Text._syncContent which reads A from the DOM node. The B character isn't there yet, so _syncContent misses it and only sees the characters A. When blurring the input node, it'll revert back to the last cached content A.