From the limited description this sounds like a known LibreOffice bug that was current about the time this report was originally posted.  It was posted on LO bugs at least twice & was marked as a blocker.  I experienced it myself.

LibreOffice had been given an option to use the desktop environment's own open file dialogs.  This option was the default.  It didn't work under KDE3 and it's to be expected that the same would be true under TDE.

The KDE3 workaround was to go to Tools>Options>LibreOffice>General and tick the box to use LibreOffice dialogs and OK.  I can confirm that this workaround worked for me.

This has been fixed in later versions of LO by removing the option - the tick box is no longer there & only the LO dialogs are used. LO 3.3.4 is working for me under TDE 3.5.13.

Extra information.

The environmnet variable OOO_FORCE_DESKTOP influences behaviour.

By default this is assumed to be kde4.  In this setting LibreOffice dialogs are used and the option to change this is removed from the Tools menu and the default is to use internal dialogs.

If it's set to kde this signifies KDE3 the option is restored.  However if LibreOffice dialogs are not selected no dialog is displayed and the program doesn't terminate properly.

OpenOffice also has the option in the Tools menu under kde3 but it seems to have no effect and the OO dialogs are used irrespective of the setting.

If it's set to gnome (assuming sufficient of Gnome is installed to support this) the customisation option is on the Tools menu and either option works; if LibreOffice dialogs are not selected the Gnome dialogs are displayed.

I read that the use of KDE dialogs have been dropped from the source of both versions of Office.  It seems that in circumstances where KDE dialogs are to be used OO falls back gracefully to using its own dialogs and LO doesn't.

To set the environment variable on a per-user basis:

In terminal:
cd $HOME/.trinity
ls

If ls doesn't list a directory called env
mkdir env

Now go into env:
cd env

You need to create a file office.sh with contents export OOO_FORCE_DESKTOP=kde3
You can use your favourite editor or simply give the command:
echo export OOO_FORCE_DESKTOP=kde3 > office.sh

Now make office.sh executable:
chmod a+x office.sh

The file doesn't have to be called office.sh - it can be anything you like provided that it ends in .sh and, of course, you could replace kde3 by any other valid value.

Finally, the value of the variable affects the icon set in use on the menu bar.  I much prefer the kde3 option but YMMV.

Is this report still valid?

In LO  3.5.7.2 this o. k. nmow.

Marking as fixed per comment by original reporter.