What is the "Great Wall" bug?

I have read somewhere here about the "Great Wall" bug.

Can please someone explain to me in which consist this bug and if it's still present in the latest version of Conquest (1.22, if I remember correctly), respective in the latest version of Play the World - I am playing on one of these 2, depending if I want City View (I love these) or the new features of Conquest.

Tx in advance

Presumably you're referring to the bug that causes great wonders and/or the Palace to be destroyed by bombardment. Thing is, the first improvement that gets destroyed by bombardment is Walls; if the town has free walls (provided by the GW in C3C, I'm not sure if this effect was in PTW) then the game looks for something else to destroy--possibly a wonder or the Palace.

Edit:
and welcome to posting at CFC I see you've been a member for a while.