Weird refresh bug entering text in Safari 6?

Every now and then, I get a strange problem with Safari 6.0.2 on OS X 10.8.2: when entering text into form fields, part of the text disappears while I type and stays like that until I press the cursor arrow or click into the field - this will bring back the text I just entered. It looks like a graphics glitch - like the text fails to refresh properly. It doesn't always happen and it's not dependent on the website or on what I type. In fact, I just had it happen here on Apple Discussions while typing this sentence... While I was typing, the last word or two went blank (like whitespace) and then re-appeared as I continued to type.

Has anyone else seen this? Running a 15" Retina MBP, just for the record.