deadlock при drop index concurrently

Вот что видим в логах:

Mar 23 15:45:07 mdb postgres[26481]: [177-1]
user=pgsql,db=geo,client=10.77.255.13 ERROR: deadlock detected
Mar 23 15:45:07 mdb postgres[26481]: [177-2]
user=pgsql,db=geo,client=10.77.255.13 DETAIL: Process 26481 waits for
ShareLock on virtual transaction 8/29343079; blocked by process 15087.
Mar 23 15:45:07 mdb postgres[26481]: [177-3] Process 15087 waits for
AccessExclusiveLock on relation 24694 of database 17701; blocked by process
26481.
Mar 23 15:45:07 mdb postgres[26481]: [177-4] Process 26481: DROP
INDEX CONCURRENTLY IF EXISTS geo_11_2gis_get_route_platform_ids_from_json
Mar 23 15:45:07 mdb postgres[26481]: [177-5]
Mar 23 15:45:07 mdb postgres[26481]: [177-6] Process 15087: LOCK
TABLE geo_11 IN ACCESS EXCLUSIVE MODE
Mar 23 15:45:07 mdb postgres[26481]: [177-7]
user=pgsql,db=geo,client=10.77.255.13 HINT: See server log for query
details.
Mar 23 15:45:07 mdb postgres[26481]: [177-8]
user=pgsql,db=geo,client=10.77.255.13 STATEMENT: DROP INDEX CONCURRENTLY
IF EXISTS geo_11_2gis_get_route_platform_ids_from_json
Mar 23 15:45:07 mdb postgres[26481]: [177-9]

кто-нибудь может объяснить откуда мог взяться при указании конкурентности
дедлок?
версия postgres 9.4.4
--
С уважением,
Вавржин Игорь