I was using a virtual call to the base class method and a mutable BaseClassReference as "this" instance.
The result is a callvirt to the base class method in CIL that is translated in a this.Method() call in C# by Reflector.
I disassembled a base.Method() call emitted by the C# compiler and it's a plain (non virtual) call to the base class method.
Probably reflector is confused because I mixed things up.
What should be the correct way to write a base.Method() call in with CCI?