Greetings,
 
I found the mistake. As this may be useful to others the details are as follows:
 
In the source file 
    derived_j/derived_j.R
of every derived class the source of the base 
    source("..base/base.R")
was included (as you would in C or C++).
This file contains the statement
setGeneric("showsSelf",...)
 
However when doing in file tests/test.R
 
source("../base/base.R")source("../derived_1/derived_1.R")source("../derived_2/derived_1.R")
....source("../derived_n/derived_1.R")
 
the repeated evaluation ofsetGeneric("showsSelf",...)
is triggered.
 
Apparently after each such call to setGeneric the slate is wiped clean
and the previous definitions for methods of the generic deleted.
Thus only the last definition in 
 
 
source("../derived_n/derived_1.R")
survives.
The inclusion of source("..base/base.R") is not needed
and removal cures the problem.
	[[alternative HTML version deleted]]

