It is possible that the builder has not used an appropriate method of fixing tiles, namely "dot & dab". This is where a number of spots of adhesive are put onto the wall and the tiles are then pressed into these.
Dependent upon the weight of the tiles and the surface they are being affixed to, there are British Standards as to the type of adhesive and the adhesion of tile to adhesive. If your installation is part of a new build there is no reason why the builder could not ensure the correct process is followed, just as the work I start tomorrow Monday, where I need to use a rapid setting adhesive onto plain plaster-board walls.
Layout is the most important element when including a border. As the border costs you significantly more than the ordinary tiles I try not to run the border through where the shower valve is fitted. This does not mean you will get a leak. There are many customers who have their whole bathroom tiled with mosaics and never have a problem. Also, if the tiles are standing so far off the wall the installer should be using mosaic spacers behind the tiles to make sure they are level with the other tiles and also flat.
With the shower you can apply a tanking membrane that will help to reduce the potential for major damage if there is a leak.