This issue was detected in LibreOffice 3.3 RC1 on Windows XP.
Here is the process to reproduce the issue:
1. Add an image to the document through the menus: Insert > Picture > From File...
2. Right-click on the image and select Description from the context menu.
3. Fill in the fields Title and Description.
4. Quit the Description dialog by pressing OK.
5. Right-click on the image and select Caption from the context menu.
6. Fill in the Caption field; quit the caption dialog by pressing OK.
7. Right-click on the image (i.e. on the image inside the frame created by the
caption, as opposed to a right-click on the frame itself), and select
Description from the context menu.
8. The fields Title and Description (filled in at step 3) are now empty.

Note: the issue also appears when adding only the Title or only the Description.

Current workaround: add the caption first, and then the Title and Description. (The title and description don't disappear if the caption is modified afterwards.)
Few people will be aware of the disappearing Title and Decription and think of
the workaround.
The title and description are needed for blind users (or any screen reader
users) and for exporting to audio books (e.g. in the DAISY format, with the OOo/LibO
extension odt2daisy). In other words, it's an accessibility issue.

Note: this issue was also reported in an OpenOffice.org bug and fixed very quickly; see http://qa.openoffice.org/issues/show_bug.cgi?id=115719