Return value of getClasses() in R?

Question

getClasses() returns the all the classes visible from the calling function, the return value is in the "character" class.

However, it is different when directly displaying the structure of an return values and when displaying the assigned variables. Why is that? (see the following code)

str(getClasses())
#chr(0) 

all_classes <- getClasses()
str(all_classes)
#chr [1:128] "refMethodDefWithTrace" "numeric" ...