Did Valve break the block feature?

As some of you know, in order to prevent certain people from joining the same servers as you, all you needed to do was to block them on steam.

However for a few days now this feature seems to be disabled. I see a lot of cheaters on official servers popping up and ruining everyone's game, even though I had them blocked for months! I met other players that also shared their disturbance with this situation. Blocking them again doens't do anything and they are able to freely connect to your lobby or a game in progress.

I wonder if this is a glitch in the last update or Valve had deliberately disabled it.