http://test.winehq.org/data/fba08e34c4478fdce5055c5c3ead7d8958875bae/#scrrun...
This one is a surprise to me. Instead of a normal BOM sequences it writes this:
--- filesystem.c:1359 http://source.winehq.org/git/wine.git/?a=blob;f=dlls/scrrun/tests/filesystem.c;hb=fba08e34c4478fdce5055c5c3ead7d8958875bae#l1359: Test failed: got L"\f896\200f" ---
0x200f is RTL mark, but 0xf896 is a private are codepoint, with no standard meaning, so it's probably something else encoded.
This only happens on Hebrew locale (and probably others RTL). With Japanese it looks like "\f8f3\f8f2", search shows me some ShiftJIS -> UTF translation results, that mention these codes as exactly 0xff/0xfe substitutes. Probably Aric knows more about that.