When you save a protected ODF file using a password, the preview thumbnail in the Start Center should not show a small part of the first page but a generic icon.
LO 4.2 had the right behavior, showing a generic writer, calc, impress... icon when the file is protected by a password. But, starting with version 4.3 (first alpha release and up to 4.3 RC3), the preview thumbnail is shown. This is illogical as it shows a small part of a file that is supposed to be confidential.
I may also add that the preview thumbnail (thumbnail.png) is usually too big in Linux (cant't say for other platform). The thumbnail.png file in the ODF archive increased by 30 kb between version 4.1 and 4.2 (and up) of LO. Of course, that is marginal in a big file, but when the ODF file is small, the increase in size is too big and the total archive (the resulting ODF) is too big for nothing.
*** This bug has been marked as a duplicate of bug 80755 ***