last_analyze/last_vacuum not being updated

I'm looking at a case on 9.4.1 where the last_analyze and last_vacuum
stats for a handful of tables seem stuck.  They don't update after
running an ANALYZE or VACUUM command, and they don't react to
pg_stat_reset_single_table_counters().  All of the affected tables are
system catalogs, some shared, some not.  Other system catalogs and other
tables have their statistics updated normally.  Any ideas (before I try
to blow it away)?