PickSplit method of 2 columns ... error

Has anyone come across this error before?

LOG: PickSplit method of 2 columns of index
'asset_position_lines_asset_cubespacetime_idx' doesn't support secondary
split

This is a multi-column GiST index on an integer and a cube (a data type
from the postgres cube extension module).

I traced the error to the gistUserPicksplit
<gistsplit_8c.html#ae6afe3060066017ec18f7d40d3f9de8> function in the
gistsplit.c ... I surmise that this method is called whenever a page
split is necessary.

So, I know when this error occurs, but I don't know why.

Thoughts anyone?
Cheers,
Kevin

--
Kevin Neufeld
Software Developer
Refractions Research Inc.
300-1207 Douglas St.
Victoria, B.C., V8W 2E7

Phone: (250) 383-3022
Email: kneufeld(at)refractions(dot)net