After researching Trading; although i delayed building Merchantcross Bazaar in an existing town to wait for an outpost to upgrade into a town.

Upon reaching town status, I tried to build the Merchantcross Bazaar; but the option was no longer available.  Several turns later I get a message that another nation has just completed the Bazaar.

Not sure if starting the project disables all other nations from starting the same project is WAI or a bug.  If not a bug, this can easily be used to 'lock' up an achievement by a nation by only queuing the project, only to have the project be moved to a more suitable location at a later time.