#1

In the formulas that gather or calculate data from a sheet other than the sheet that the formula is written on the reference to the sheet is lost on save. Eg. - =SUM('sheet 2.C3:C6) after saving and opening again will appear as =SUM(#REF!!C3:C6)
I have saved sheets in XLS, Xlsx, open office ods.
,!! I just saved sheets in xls and the formulas remained intact ???
The border formatting is still lost in certain parts of the sheets.

#2

Do not include spaces in sheet names. Rename Sheet 2 as Sheet2, Sheet_2.

#3

Verified the issue about broken formulas in xlsx format, reported a bug:
Saving as xlsx breaks formulas with sheet name in the references

Last version working fine:
Version: 4.2.0.4 Build ID: 05dceb5d363845f2cf968344d7adab8dcfb2ba71

In relation with lost borders, there is a resolved bug for next releases:
Cell Borders not exported properly to XLS

I think if you don’t need the new features of 4.2.x, better stay with the more stable version of 4.1.x series, you can find it in download page or you can find all releases to download in :All LibreOffice releases

#4