I tend to use Preview a lot when writing posts - trying to minimise any embarrassment I feel when reading previous posts by myself, it doesn't always work

. For some time now (I can't say exactly how long, sorry) I have noticed that sometimes I get extra stuff (a copy of text from earlier in the post) appended to the text in the editor after I've hit preview.
It doesn't always happen, but I noticed it again tonight when I was replying to
this post from HarryT. At one point, after hitting preview, the word "road" was appended to the text in the editor. I removed it and kept going. But now when I try it I can't get it to do it again. I'm wondering if it only happens at certain lengths or something.
Are you aware of a problem like this? If so I'll continue as I am until it is fixed, if not then I will try to remember not to ignore it when it happens next and post an example here.