At least an upside of the server lag..

[Flandria4]

Simultaneous building: ON

[Tage]

Same thing happened to me...
However, the first mine I was building never appeared in the building queue and never needed a building licence...
...until after a refresh following a "cannot connect to server".

At that point both mines were built and both licences taken. But to build without needing a slot in the queue was fun...