I added few dozen words on custom dictionary. I use the words so often that they now work as word flow (or whatever its called). You know, you type one word the rest appear one by one.. Love it. I too added few mistyped words by accident and now even if I Type the word correctly the one from dictionary replaces it. So I have to erase that and retype. Frustrating.
If I clean whole dictionary, I might lose the word flow. So, waiting for MS to allow us edit dictionary