As the title says when an editor pastes text into a single-line field in the experience editor, the html formatting does not get stripped correctly. This bug has been verified in Sitecore 8.1 and 8.2. I have not tested in any other versions.
What I have done here is to change the field type in the home item of an empty Sitecore installation to a single-line field. I then searched for “Sitecore rules!” and copied+pasted the title from google into the single-line text field and saved the item.
There is a patch for this provided by Sitecore support. It can be downloaded here:
When applied the html stripping of formatting should work as intended.
The version of the patch says that it is built for Sitecore 8.2, but Sitecore support has told me that it will work fine for Sitecore 8.1 as well.