pt-query-digest doesn't properly aggregate by db when using --output=json

I'm using pt-query-digest on a MySQL instance with multiple logical databases. When I run pt-query-digest in the normal (text based) output mode, for common queries like "COMMIT" that appear across I see them properly reflected in the output:

# Query 5: 142.78 QPS, 0.07x concurrency, ID 0x813031B8BBC3B329 at byte 18549436
# This item is included in the report because it matches --limit.
# Scores: V/M = 0.00
# Time range: 2015-02-04 22:05:15 to 22:05:24
# Attribute pct total min max avg 95% stddev median
# ============ === ======= ======= ======= ======= ======= ======= =======
# Count 6 1285
# Exec time 3 658ms 16us 16ms 512us 839us 770us 596us
# Lock time 0 0 0 0 0 0 0 0
# Rows sent 0 0 0 0 0 0 0 0
# Rows examine 0 0 0 0 0 0 0 0
# Rows affecte 0 0 0 0 0 0 0 0
# Bytes sent 0 13.80k 11 11 11 11 0 11
# Merge passes 0 0 0 0 0 0 0 0
# Tmp tables 0 0 0 0 0 0 0 0
# Tmp disk tbl 0 0 0 0 0 0 0 0
# Tmp tbl size 0 0 0 0 0 0 0 0
# Query size 0 7.53k 6 6 6 6 0 6
# String:
# Databases sentinel (889/69%), locket (94/7%)... 11 more
# Hosts 10.30.33.27 (199/15%), 10.30.27.22 (195/15%)... 55 more
# Last errno 0
# Users sentinel_r... (889/69%), locket_rw (94/7%)... 11 more
# Query_time distribution
# 1us
# 10us ################################
# 100us ################################################################
# 1ms ##
# 10ms #
# 100ms
# 1s
# 10s+
commit\G

As you can see above, several databases are listed for COMMIT. All fine and good. When I try with --output=json though the information is lost (output is shown with a bunch of stuff trimmed):

pt-query-digest --output=json tmp-slow-9fdef21f.log | python -m json.tool | less

        {
            "attribute": "fingerprint",
            "checksum": "813031B8BBC3B329",
            "distillate": "COMMIT",
            "metrics": {
                "db": {
                    "value": "vorenus"
                },
                "host": {
                    "value": "10.31.4.95"
                },
                "user": {
                    "value": "vorenus_rw"
                }
            },
            "query_count": 1285,
            "ts_max": "2015-02-04 22:05:24",
            "ts_min": "2015-02-04 22:05:15"
        }

I'd like to ideally get the data broken out by logical database, or if that's not possible/difficult then at least I'd like to see that the query affects multiple databases.