This is not strictly a portable versions query, but rather I think it must be something core to these respective programs.
I have and have used both of these suites for quite some time. (Because I like to have available alternatives on hand in many cases, rather than relying on just a single program in a given category.) But this will refer to the most recent portable versions of each. Another possible way of stating the Subject Header above would be, "Has Something Fundamentally Changed in Open Office and How It Works in Handling Spreadsheets ?" I have a number of longstanding database type spreadsheets (descriptive lists, covering pertinent info of one sort or another), which are maintained by an associate for me. They are saved as both .XLS format (rather than MicroSoft's subsequent .XLSX format), and in some cases also in the native Open Office format. (.OSD ? I don't recall the name precisely.) When I try to open any of them now in Open Office, what I see onscreen I would describe as useless gibberish. I don't know if there is any facility for uploading screenshots to the forum, but if necessary I could Copy & Paste a sample from this. Anyway, in stark contrast, if I instead open any of these spreadsheets in Libre Office, I will still see just what was expected: all the Rows, Columns, and proper data within -- fully intact. Rendered properly in the latter suite, but not at all in the former.
I guess the obvious, short answer is: "Then just use Libre Office, instead." But I'm left wondering whether some key standards may have changed somewhere along the way, with Open Office just not keeping pace ? If anyone seeing this is sufficiently familiar with the spreadsheet module of both suites -- maybe even down to a development level -- perhaps they could shed some light on this ? It does present a rather glaring discrepancy.