My washer will sometimes overfill.. and sometimes not. What would cause that?

Hi Belle and welcome to The Plumbing Page at ANHD.com. You're responding to a 7 year old dead threads so I gave you one of your own. Please check the date before you post. Thanks
Please explain where it's overflowing from. Does it not quit filling and overflow the top or does it back up out of the stand pipe when draining? Back to you, Tom