SEXP i/o, .Call(), and garbage collection.

One possible reason for such problems is if you copy the pointers
for say, attributes, classes, names, rather than duplicating them.
With very few exceptions, mostly in classes, no two R objects of
the sort you normally encounter/create/play-with should share *any*
part of their data-structure. e.g. such problem can result if you
assign the row names of the input to the output (even if both have
the same row names).

Hmm.. I thought that using setAttrib() would automatically increase the 
reference count, right ?

In particular, I quite often use "pseudo-factor" string vectors - where the 
string objects are passed through cache and reused when forming a string 
vector. The result is true character() type but with considerable memory 
savings. The downside is that R reference count field is usually saturated.

                                best

                                    Vladimir Dergachev