Not sure if this is a bug, or if this is by design, but it looks very odd (at least to me).
Create an index with two descending columns, it is listed twice in table view.
CREATE TABLE DOUBLE_DESC_T (COLA NUMBER, COLB NUMBER);
CREATE INDEX DOUBLE_DESK_I ON DOUBLE_DESC_T (COLA DESC, COLB DESC);

(Note probably is same behavior in current non-EA version, no time to check right now).