Actually, the answer may be more simple. Guessing, that gmaps switches to drawing vector data at a certain zoom instead of rendering the road line vector data

Actually, the answer may be more simple. Guessing, that gmaps switches to drawing vector data at a certain zoom instead of rendering the road line vector data to the TMS tile. This simply means that the version of the vector data used to draw at the increased zoom is the older version but is actually being used to draw the roads on the browser instead of rendered into the tile before transfer.