This is intentional. I mentioned it in the update note:
"Filters now appear at the root of the list, which means they work for all categories (apparel, weapons etc.) However, there is no way to collapse them into a submenu anymore."

The way the "SpecialThingFilterDef" get shown in a menu changed when Rimworld got updated to 1.1, so I couldn't make it work in a separate dropdown menu anymore.

The upside to this is, that the filters will now work for EVERY category, not just Apparel.
The downside is, that the menu looks a little cluttered now :(


I was thinking about putting the filters in a separate window, but I'm currently not playing Rimworld anyway, so it might be a while until I get it changed. Also, I don't know, how to do it yet :D

@Kami Katze
Thank you for your answer. I understood that.

Be careful

The mod can slow down your game really hard in menus with ingredients(Bill's menu where you choose what to use to craft/surgery)

and if you remove it later it will break every single possible bill in the game (It will think that the map has no ingredients for any craft/surgery)