If you are modifying the master for "a supposed slave" site, this probably mean that you are not connected on the slave but on the master.
To ensure that you are logged on the master or on a slave, put different website title that you can check.
A possible reason why you reach the master is that because you didn't write the domain name as you have specified in the "manage site" corresponding to the slave.
For example, you enter a URL without the WWW and in your slave site definition you just have provide the one without the www.
Check also that you spelled it correctly. The domain name is case sensitive.
If you want to have users that have both access in a master and in a slave site, you have to share the users when you create a slave site.
See for example the tutorial video 16 that show how to share the users.
You can also do it with the master (instead of the slave 1) as shown in the video.
www.jms2win.com/en/tutorial#jms12x-16