Actually, it seems to be happening with other html as well, and not with copied text or in rich text fields. I corrected the form entry that I originally posted about, but here's a screenshot of a form entry that I haven't edited for over a week:
It seems as though some css and html is bleeding through into random places.
Here's my preview link:
The screenshot above is taken from the collection titled "Quotes", form entry "(Publication) SWPP - Managing Schedule Exceptions"
Here's another from the same collection:
And another issue from a different collection (case studies):
Now, it doesn't seem as though my live site is affected all that much, but the form entries being wrong are confusing for my content editor and I did have a text string filter set up that broke when the & was changed to an &.
Overall, not a life altering bug, but still strange.