Weird problem when writing in compose mode

In compose mode, when I’m typing sometimes a white line will run through the line 3 lines above the line I’m typing on. It disappears the second I stop typing and comes back when I start again. I checked and this problem doesn’t occur in ms words full screen mode so I don’t think its my computer. Anyone know what the deal is?

Does it kind of look like an overstrike has been inserted in the lines? If so that’s a known rendering problem with the text drawing system we use. Steps have been taken to mitigate it, by forcing refreshes at the expense of performance, but the initial appearance of them will still happen under certain scenarios. Something that has been known to trigger this bug is odd-numbered zoom factors for the text. If your composition mode is zooming to say, 175%, the problem can sometimes be avoided by setting the zoom to 150% instead.

Microsoft Word uses a completely different text rendering engine than the base Mac system. It has been developed my Microsoft and shares no common code with how Scrivener (and indeed many OS X software) displays text.