I use Swype so I may be wrong but... If you spell out your word and press space without clicking on it it will be auto corrected. We know that for sure. But, if you spell out your word and click it in the top left part of the keyboard it turns blue so it is in the dictionary now. So from now on you don't have to click that word anymore, Just type it completely and it's there. I believe it was not programmed to auto correct out predictive text user words Due to the challenge of assigning words priority over each other.
if you want your words auto correct/predicted maybe try after market?
Good luck,
John