Just updated from LO 4.2.2 to LO 4.2.3. Language: gl (Galician). OS: Windows 7.
I do not see table borders on my odt documents (saved with previous LO versions).
I also tried creating a new document with a table, and borders do not appear, either.
Any idea? Thanks.
Check the Table creation defaults:
Tools - Options - LibreOffice Writer/LibreOffice Writer/Web - Table
Reference: Table - LibreOffice Help
If this does not work:
Can you add and remove borders on existing tables?
Probably Bug 76195 - regression: with “Table Boundaries” disabled, the borders of tables are not visible
Status: RESOLVED FIXED (LibreOffice 4.2.4).
Workaround:
Menu Table → Table Boundaries (enabled).
I also believe it is that bug. And the workaround works… 
Thanks!