Which admin address in a multistore configuration?

[OswaldRunner]

Hello,
I am running a multistore (1.5.6) and before writing this, I have approached BO only using "default shop"-admin address.
Like "www.defaultshop.com/administration".
Suddenly, a module created by software developers for me, doesn´t show up as a tab under "catalog/products" any longer.
Of course I complain about this to my developer, and he says it is visible at his side.
After clearing cache, removing web history, uninstalling and installing the module many times, we find out that my developer is approacing BO by going to the address belonging to the shop where the module must be active.

So instead of "www.defaultshop.com/administration" he uses "www.actualshop.com/administration".

"Actualshop" is a shop in another group than "defaultshop" in the Multistore system.

One magic thing is that the module is installed in "defaultshop" mode. Not "actualshop".

Before this I didnt know you could use different addresses to approach admin, I thought the whole idea with a multistore system was that you could administrate the system from one address, but obviously, now is proven, there is some differences depending what address you use.

My question is:

Should I always use admin address depending on what shop I want to administrate, or "should" it not matter?
Can anyone explain differences?

Thanks
Anders