When you host a server with Fillcan, it screws up your $face settings for the purpose of a randomization algorithm made so that whenever you fillcan someone with an FX, their face changes. I fixed it by going through the fillcan server.cs and find-and-replacing all instances of "$face" with "$randFace", but barring this shyGriff's suggestion also works.
I've had this problem for ages, and I just fixed it now after finding an old thread where someone said that fillcan was the cause of the problem. The problem didn't occur until I started hosting, and persisted until I reset blockland, even if I shut down the server. Fillcan still seems to work using my find-and-replace solution.