Does anyone know??????

I will try to explain this the best I can please bear with me. SOMETIMES when I type (in an Email Letter) for instance, if I make a mistake and catch it before I finish the email, (and I go back into the paragraph) and backspace to correct the miss-spelling, I have to rewrite the whole thing from the beginning of the word forward untill I get to where I can continue with the email. This also happens in Word Pad too. This only happens sometimes, and it is a hassle to have to rewrite the whole thing over. Say I have a Sentance in the first part of the Paragraph, and I go back to that Sentance to correct a misspelling, and if the Paragraph is, lets say, ten (10) Sentances long, I have to retype the whole ten (10) Sentances. I hope I am making sense. Thanks for any help.