With latest version 45.0.0.1187 the borders of merged range are not copied correctly.
With this sample code:
var ef = new ExcelFile();
var ws = ef.Worksheets.Add("1");
var range = ws.Cells.GetSubrangeAbsolute(1, 1, 2, 2);
range.Merged = true;
ws.Cells[1, 1].Style.Borders.SetBorders(MultipleBorders.All, SpreadsheetColor.FromArgb(0,0,0) , LineStyle.Thin);
range.CopyTo(1, 4);
ef.Save(@"c:\temp\test.xlsx");
This merged cell borders issue was resolved and the fix is now available in the latest publicly released bugfix version for GemBox.Spreadsheet.
Visit our BugFixes page or NuGet.