a strange output from vacuum

Hi all,
I have (recurrent) cache lookup pb in my db and I
didn't find out the solution yet. But, doing a vacuum,
I got the following :
db=# vacuum;
NOTICE: RegisterSharedInvalid: SI buffer overflow
NOTICE: InvalidateSharedInvalid: cache state reset
VACUUM
I have no ideas about possible correlation...

Moreover, and may be of little help, here is a
fragment of a vacuum verbose: this thing seems to be
thrown when vacuuming pg_attribute.

NOTICE: --Relation pg_attribute--
NOTICE: Pages 48: Changed 21, reaped 26, Empty 0, New
0; Tup 2147: Vac 1590, Keep/VTL 0/0, Crash 0, UnUsed
0, MinLen 98, MaxLen 98; Re-using: Free/Avail. Space
160560/160560; EndEmpty/Avail. Pages 0/26. CPU
0.00s/0.00u sec.
NOTICE: Index pg_attribute_relid_attnam_index: Pages
152; Tuples 2147: Deleted 1590. CPU 0.02s/0.01u sec.
NOTICE: Index pg_attribute_relid_attnum_index: Pages
64; Tuples 2147: Deleted 1590. CPU 0.01s/0.03u sec.
NOTICE: Rel pg_attribute: Pages: 48 --> 28; Tuple(s)
moved: 1536. CPU 0.00s/0.12u sec.
NOTICE: Index pg_attribute_relid_attnam_index: Pages
153; Tuples 2147: Deleted 1536. CPU 0.02s/0.02u sec.
NOTICE: Index pg_attribute_relid_attnum_index: Pages
66; Tuples 2147: Deleted 1536. CPU 0.01s/0.01u sec.
NOTICE: RegisterSharedInvalid: SI buffer overflow
NOTICE: InvalidateSharedInvalid: cache state reset

Has anybody seen such a thing before ?
Thanks,

Jeff.

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