I don't even know how this center accross selection  works. And I have the feeling it doesn't really anyways:

E3: 'Hello'
select E3:F3 and choose 'centre accross selection' 
I understand that the 'Hello now looks like it is centered on E3:F3.
select G3 and choose 'centre accross selection'
Considering that I didn't do anything that seems to affect the 'Hello' why is the 'Hello' moving?

I am quite sure that while we can save this in ODF, there is surely no native way to do that.

./ssconvert ../samples/merge.gnumeric ~/mmm.xlsx
localc ~/mmm.xlsx
# save as ~/mmm.ods

This produces *something* that looks like center-across-selection.
This is probably what LO considers closest to c-a-s.

LO merges the cells in questions and and centres the content:

 <table:table-cell table:style-name="ce2" office:value-type="string" calcext:value-type="string" table:number-columns-spanned="4" table:number-rows-spanned="1"><text:p>Center Across</text:p></table:table-cell>

Is that what we want to do?

Excel matches the behaviour of comment 1.

Merging and centering is probably the closest we can get.  Roundtrip
will fail, but the test can be beating into submission.



From http://thenewpaperclip.com/2008/04/15/center-across-selection-the-merge-and-center-alternative-in-excel-2007/
"It’s just like merge and centre, but without all the hassles that merging cells cause."

While round-trip is fixed we are not yet exporting it in a way LO can handle. We can do this in a way that round trip remains happy.

This problem has been fixed in the development version. The fix will be available in the next major software release. Thank you for your bug report.