Any tab characters which show in the file diff view are rendering as visible characters, overlayed on top of other text.

Worse (and more bizarrely) a tab at the end of the last line of the file causes the diff view to completely hide that line. See screenshot (there is a tab character after the word "after").

Font is set to Consolas, 11pt, in case that's relevant. The effect persists regardless of Windows vs Unix line endings.