It's weird, I just sort of know if a word is spelt correctly or not

I have this too. Do you also recognise this : somebody else has written a text and asks you to read it. And even if there is only one spelling mistake in that entire text your eyes are magically "drawn" to it. It's like I don't even have to read the text to see the fault.

Funny thing, but I've been able to do this for as long as I can remember.