That usually happens when you edit but if you submit your answer and it is jumbled or not all there try using the F5 refresh key, that clears it on edit.
Are you using a telephone or a real computer? I suspect many internet sites, such as yahoo, are reconfiguring to adapt to people using smartphones. I use a laptop and have not had this problem. Plus, it is difficult for the software coding geeks to design programs and interfaces which can be used by totally different platforms like I-phones and Androids. This may be part of the confusion, even for us who use real computers.
THE EASIEST thing to do is write you words in an email to your self, send it to your self, then copy those words ,and paste them into you question on yahoo answers