In Delphi, passing the URL like this should sort it: PAnsiChar(AnsiString(url))
That's exactly what I'm doing (the url is PAnsiChar type, and it's converted one line before call) - it works for HTTP streams and not for MMS.
Probably, that's the issue with BASSWMA, looks like it somehow considers the UNICODE flag.
Anyway, I already sorted this out, by not adding this flag... But I'm still interested where the bug is