Designing Kitchens and Bathrooms - Do I need to seal entire modern shower cabinet?

I bought a house that was renovated before I moved in. I have since discovered that a very modern shower cabinet is leaking water :( There is silicon sealant around the outside of the doors but I have discovered that water leaks where the shower pan meets the two back walls. When I point the shower at the bottom towards the wall the water just falls behind it and on the floor underneath! I read that modern shower cabinets do not need to be sealed so I don't understand why I have this problem. The cabin looks correctly installed.
Should I seal the back walls as well, and if so is it bad to do it from the inside? There is no way I can obviously get in behind!
Thanks in advance!

Welcome to the forums! Not too sure how it was installed, but you shouldn't have running water on the floor. Could you post a couple of pictures on a site such as photobucket.com and copy/paste the HTML code to a reply post? That way we can see what you see.

Thanks for the promt response Chandler!
You can see some photos on:
http://showerellen.shutterfly.com/
On the photos you will see
1. Entire shower
2. Close ups of the bottom of the back walls (where it meets the tray- this is where I want to put silicon
3. Underneath the shower- where you see the white wall that is where the water comes down when I point the shower head against the back walls (as point 3)

The reason I ask is because I read that you should only place it on the outside of the shower- not sure why....

Hope that helps!
Thanks again