Context override?

In my zapata.conf, I have the context set to “Default”. When I use the asterisk gui to add a service provider, it enters this into the user.conf file:

signalling = fxs_ks
callerid = asreceived
context = DID_trunk_1
canreinvite = no
group = 1
hasexten = no
hasiax = no
hassip = no
trunkname = Ports 1,2,3
trunkstyle = analog
zapchan = 1,2,3

Why does this cause the context that is in the zapata.conf for these channels to be overridden and now use the [DID_trunk_1]?

Where can I find out more about this?