Related to 75130 but is still present in 220.127.116.11.alpha of 20-Aug-2014:
I draw a border in LibO. I save as .xls or .xlsx. I open the file in Excel (2010, on Windows). The border shows up as a dotted line.
The message thread re. 75130 indicates it is an issue of line thickness. As a minimum, set the LibO defaults such that Excel produces borders similar to the one drawn in LibO. Better yet, ensure that >solid< borders drawn in LibO >never< become dotted ones in Excel.
This is independent of .xls or .xlsx file format. Also fairly independent no the version of Excel used (Excel 2004 Mac produces the same dotted border).
*** This bug has been marked as a duplicate of bug 79787 ***