multicolumn GIST index question

Did anyone get multi-column GIST indexes working using both
the gist_btree and postgis modules?

It seems to work fine for me on small test cases (shown
at the bottom), but seems to crash my database for large
ones. Any advice is welcome - including pointers to better
lists to ask questions like this.

Output showing a crash (on a large database) and a
successful run on a tiny one follow.

Ron

fl=# -- sessionid is a text; the_geom is a GEOMETRY
fl=# create index testidx2 on user_point_features using gist
(sessionid,the_geom);
server closed the connection unexpectedly
This probably means the server terminated abnormally
before or while processing the request.
The connection to the server was lost. Attempting reset: Succeeded.
fl=#
fl=#
fl=#
fl=# create table test3(a text, b text, c text);
CREATE TABLE
fl=# select addgeometrycolumn ('','test3','the_geom','-1','POINT',2);
addgeometrycolumn
--------------------------------------------------------------------------
public.test3.the_geom SRID:-1 TYPE:POINT DIMS:2
geometry_column fixed:0
(1 row)
fl=# create index idx_text_text on test3 using gist (a,b);
CREATE INDEX
fl=# create index idx_text_geom on test3 using gist (a,the_geom);
CREATE INDEX
fl=#