I have two MS-Excel example documents that show lots of spreadsheet tabs when I
open them by (for example) clicking on the file icon in the file browser.

However, if I start OpenOffice.org as a server process ("soffice
-accept='socket,host=0,tcpNoDelay=1,port=8100;urp'") and upload any of these
files by using an UNO connection, I can see (visually and by calling
"xSpreadsheetDocument.getSheets()") only one spreadsheet in the document, which
contains only one empty cell. In the shell where I started the server processs,
the following lines appear:

Warning: at xsl:stylesheet on line 32 of
file:///usr/lib/ooo3/basis3.0/share/xslt/import/spreadsheetml/spreadsheetml2ooo.xsl:
  Running an XSLT 1.0 stylesheet with an XSLT 2.0 processor
Warning: on line 4470 of
file:///usr/lib/ooo3/basis3.0/share/xslt/import/spreadsheetml/spreadsheetml2ooo.xsl:
  Creating an attribute here will fail if previous instructions create any children
Error
  com.sun.org.apache.xerces.internal.impl.io.MalformedByteSequenceException:
Invalid byte 2
  of 2-byte UTF-8 sequence.

(These lines don't appear when I start OpenOffice.org regularly and open the
files in the file browser.)