After some head-scratching moments and some investigations, I found that UTF-16 BE and LE are saved with BOM.
As BOM is optional (cf http://www.unicode.org/faq/utf_bom.html#BOM), any plan to support saving without BOM?
Or at least, in the time being, state it clearly that BOM is written to file in the online doc and in menu item, so people don't have to guess and try.