My cousin had a thing similar to this, whereas she would pronounce words incorrectly : for example, she'd ask for a "frink" instead of a drink, which was really frustrating. She had loads of test on everything that it could be associated with and came back normal, and it was only when my uncle got a specialist to in did they realise that she had a small problem with her hearing. She had a small operation, I think it was just something like Gromits, and some speech classes and she now has almost perfect speech.