Thanks for the list of thing to check buddy, I'm on my tablet at the moment but when I get back on my PC I'll go through them and rule things out.
As for whether it is the character or the 15th letter, I believe it is the character. I have tried the alphabet from a different point and I've also tried just those affected characters on their own and the same thing happens, I get the dim bar across the whole row and anything after is scrambled.
Thanks for the help thus far though, I'll do some more troubleshooting tomorrow hopefully!