go to Tools- Options, LibreOffice - view and choose "Oxygen" as icon style.
close and restart libreoffice, so that the startcenter is displayed.
-> old (S-curve) document icons are used.
found with LibO 3.3.1 on Windows and Linux RPM 64bit
Let's collect icon update issues under the fdo#33229 bug - that said, I wonder whether we should unconditionally use the new icons for all icon sets - they may not fit so well visually? See also discussion on the design list.
*** This bug has been marked as a duplicate of bug 33229 ***