GIN logging GIN_SEGMENT_UNMODIFIED actions?

Hi,

trying to debug something I saw the following in pg_xlogdump output:

rmgr: Gin         len (rec/tot):      0/   274, tx:          0, lsn: 1C/DF28AEB0, prev 1C/DF289858, desc:
VACUUM_DATA_LEAF_PAGE 3 segments: 5 unknown action 0 ???, blkref #0: rel 1663/16384/16435 blk 310982
 

note the "segments: 5 unknown action 0 ???" bit.  That doesn't seem
right, given:
#define GIN_SEGMENT_UNMODIFIED    0        /* no action (not used in WAL records) */

Greetings,

Andres Freund