With LO 5.2 template browser has been redesigned. Until LO 5.1 a selection of template group (e.g. "My Templates", "Business Correspondence") was possible prior to displaying template previews. Since LO 5.2 all templates of all template groups are displayed together.
I am not sure whether it is intended or a bug. From my point of view behaviour prior to LO 5.2 should be restored. Newly implemented tooltips are very nice and should be kept.
You are not the first one, who wants back the categories, see bug 101141.
*** This bug has been marked as a duplicate of bug 101141 ***