Occasionally my Mac will get into a mode while typing where the characters continue to overlay the previous one. It's similar to the typeover feature in Word but there it is wiping out the character following the one that is being added and as you type, the word being typed overlays the word following. Here, the cursor never moves so the character continues to type over itself. It happens mostly in Safari, but occasionally in other programs as well. If I recall it happens after editing text. I've not been able to recreate it, it just seems to happen at random, but when it happens, boy is it annoying, and hard to get it to stop. Any suggestions?