As part of the conversion to templates, the single select no longer displays HTML entities. They are instead displayed as text (meaning if you want to display an & you can no longer send & or insert a non-breaking space it will display the text ' ' in place of the character.
The attached file demonstrates the problem. Simply copy to the root of the moodle site and view the page in both clean and boost. It will display correctly in clean, but will display incorrectly in Boost. (There seems to be some conversion difference between how it is handled in Boost as opposed to clean)
To see a real-world application of how this bug is affecting moodle you can see it here (contributed plugin)