Well, my stored procedures often need to be used by:
a) IB_StoredProc
b) inside a select, as lookup table for some fields
so, if what you say to Lele is true, without SUSPEND
a) works
b) does not work
mmmm! This explains the mixed test results I've got so far.
The conservative way is to add a final SUSPEND to all SP returning values... but could this damage when called by IB_StoredProc?

Second, it's a strange behaviour, since with Fields[] or FieldByName I can retrieve output values, does not matter if SP was selected or executed, the only thing that is important is that in the second case a SUSPEND must be present. But this seems to be a Interbase/Firebird issue (effects subselects of joins), not a IBO one.
thanks for your clarifications
regards
Marco Menardi