PANIC: right sibling 2019 of block 2018 is not next child of 1937 in index "sl_log_2_idx1"

I know I don't have a lot of data right now (still looking for core dump)
Any obvious thoughts or advice until I can get more info?

Dec 30 17:41:57 db-1 postgres[28957]: [ID 748848 local0.crit] [34004622-1] 2009-12-30 17:41:57.825 CST    28957PANIC:
rightsibling 2019 of block 2018 is not next child of 1937 in index "sl_log_2_idx1" 
Dec 30 17:46:17 db-1 postgres[17576]: [ID 748848 local0.info] [34005240-1] 2009-12-30 17:46:17.279 CST    17576LOG:
autovacuumprocess (PID 28957) was terminated by signal 6 
Dec 30 17:46:17 db-1 postgres[17576]: [ID 748848 local0.info] [34005241-1] 2009-12-30 17:46:17.279 CST    17576LOG:
terminatingany other active server processes 

Database recovered itself...and autovacuum of sl_log_2 started up again with no obvious issue right afterwords.

PostgreSQL 8.2.12 on i386-pc-solaris2.10, compiled by GCC gcc (GCC) 3.4.3 (csl-sol210-3_4-branch+sol_rpath)

Oldish version of slony (1.2.10)