I am not really sure if it is normal or not, but my DD certainly goes through phases of saying things really wrong and also not saying words she had previously mastered. And like your DD she does generally say things quite clearly. These phases have always passed and she has always got back to saying them correctly. Like she used to say something like meow but then went back to just the first sound 'ma' for a few weeks before getting back to the 2 syllable meow. And she started saying dad and then barely uttered it for months, then finally got back to it and now screams daddddddddddy when he comes in the room.
I've heard people say that they reckon their kids kind of 'forget' skills when they are learning other new skills, then they come back again afterwards, and come to think of it some of our weird talking phases may have coincided with learning to walk. Perhaps your DD is brewing some amazing new skill?

So perhaps keep an eye (or ear) on it for a bit longer and see if it is a phase that passes. I think it sounds within the range of normal development but your mummy instinct is a pretty powerful tool, listen to that if you think there is a problem.