Board Game Arena

I am new to the game and thought that no identical tiles could be placed unless when the yellow knowledge tile #1 has been placed.

In my current game however I coud place a second market ?


Q: Is this a bug in the implementation on BGA ?
or
Q: If I don't place the Knowledge tile #1 in the rest of the game, will 1 of my markets be removed
or
Q: Did i get the rules wrong (in that case: what is the meaning of knowledge tile #1)
or
?

Answering my own Q:
I thought the whole board was seen as the city but I reread the rulebook. A brown area is seen as 'a city' which answers my question aobve