Problems with GLOBAL TEMPORARY TABLES (GTT)

GLOBAL TEMPORARY TABLES do not work consistently. I am not sure, if all or some of the following problems described are intended. (is it bug or feature?) Out of 2 different sessions I am able to create GTTs with same name. Out of a third session I am able to see both tables (with same name), but not beeing able to access one of these tables. I am able to delete both tables, but I am not sure, which one is deleted first. Restarting MonetDB results in a situation where temp tables are still existent, but it is not possible to drop these tables out of any session. Is it a matter of privileges?