Hopefully it's a glitch with the stock text app, but I think it maybe to do with one of the law suits Slapple took out on Samsung/Android?
There is, in the predictive text section, settings where the stock app learns words you use in Gmail, Twitter and FB, pretty useless if, like me, you don't use any of these!
I've set up a "draft" email in Gmail, and add words to this email that don't come up in predictive text, it's very long winded!
Installing another app from the market fixes the issue, like Swiftkey, but I'd rather stick with what I've got
