Hi Julien,
I am glad to see that you are using SLS IP core because I am working over here in SLS fairely new employee. :)
This is feature of Q10.1 and by default it is turned on.I m going to try to explain what is global reset according to my understanding in Q10.1.
Well,In Quartus 9.1 or earlier,you wouldnt get this reset warning because in those version,we were taking care personally about the reset stuff.
Whereas in Q10.1,they provide one feature of global reset that means if this feature is turned on,whatever the RESET that you are giving to you system (whole system),that will be considered as global reset (i.e reset to all your SOPC components).
So if you have assigned individual reset to your compoents that will b ignored because global reset is turned on. (In short "ONE RESET SIGNAL FOR ALL COMPONENTS)
If you disable this global reset then you can assign you own custom reset to components individually then it wont give you any warning but if you dont assign while disabling it then it will be again error/warning.
Hope this concept will help you little. :)