Hello,
It is a rare situation I think. no search result found.
If the string which we are going to SaveToFile contains a BOM (any?) and we use TStringList.SaveToFile(const FileName: string; AEncoding: TEncoding) then the resulting file will have a doubled BOM or an unknown BOM "ff fe ef" (in case of pure FPC). Using a Hex editor to see of course.
Can you please check?
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FPC Trunk r35106
Lazarus Trunk r53927
Windows 7 x64
Linux Xubuntu 16.04