It is appearing in the data tablespace because when you do:alter index rebuild online (for example) oracle assign temp segments in the data tablespace and rename them after completion. I used this example because oracle can not create normal segments as there is already an object (index) with that name.
Adar Yechiel Rechovot, Israel M Rafiq wrote:
Please also check why data tablespace is being used instead of temp tablespace. Hope this help. RegardsRafiq<http://windowslive.com/connect/post/jamiethomson.spaces.live.com-Blog-cns%21550F681DAD532637%217540.entry?ocid=TXT_TAGLM_WL_t2_ugc_post_022009>