A Farmer villager (Journeyman - I already traded with him and he shouldn't change his profession) used a smoker, a brewing stand, and a blast furnace as he would use a composter as a workstation. The Farmer won't use a composter again if one is placed nearby, thus keeping the other workstation.

I did a test in a creative world and the villager I spawned wasn't bugged at the beginning. Then, after I had the villager zombified and cured (I had done that to the one in my survival world too), the bug appeared

Edit: I originally discovered the bug while playing a modified version of the game, OptiFine 1.17.1. In order to ensure, that the bug wasn't caused by the modification, I tested it in a world that I had created in vanilla 1.17.1. The same problem occurred in vanilla as well