Strange 1st character when saving as text (solved)

Very strange behaviour!
When I open any .odt file and save as .txt, the first character of the first line is asc(65279) (zero-width no-break space).
Any reason for this? Can I prevent it?
A bug?

You cannot use UTF8/UTF16 and avoid BOM. Only if your text is ASCII/US, you may use that encoding and get the same bytes as UTF8 without BOM.

Thank you Mike. I was just coming back to say I had discovered that, but you beat me to it. Since I was trying to do this in a basic macro, the code is:

oArgs(0).name = "Overwrite" : oArgs(0).value = true
oArgs(1).Name = "FilterName" : oArgs(1).Value = "Text (encoded)"
oArgs(2).Name = "FilterOptions" : oArgs(2).Value = "ASCII_US,LF,,,"
StarDesktop.getCurrentComponent().StoreAsUrl(ConvertToUrl(sFileName), oArgs)